scripts/prepare_changelog: Update unescape parenthesis for improved matching

Before change
```
413e19b84 Merge pull request #8942 from desolatorxxl/google-fix-ssh-keys-metadata
b81800db2 Merge pull request #8935 from zaventh/feature/start-on-boot
94863168b Merge pull request #8922 from hashicorp/f-vsphere_iso-export-ovf-options
56aebbeda Merge pull request #8920 from rhencke/patch-1
d068430ab make sure locals are evaluated only once variables are + test this (#8918)
3dae5df6e Merge pull request #8905 from hashicorp/fix_8493
811a7304a Merge pull request #8907 from hashicorp/fix_8428
fa49d2145 Merge pull request #8906 from hashicorp/fix_8904
23f56036a Merge pull request #8889 from hashicorp/hcl2_singular_blocks
dc9259f73 Merge pull request #8892 from zaventh/feature/vga-adapter
fc35f0200 Merge pull request #8890 from hashicorp/fix_8880
7972ab723 Merge pull request #8735 from hashicorp/fix_plugin_loading
890d7b2ec Merge pull request #8875 from hashicorp/fix_8812
e94ff7019 Merge pull request #8883 from hashicorp/fix_8835
9075b807d Merge pull request #8891 from rhencke/patch-1
6477d8a0c Merge pull request #8882 from hashicorp/fix-var-file-hcl
6008f911f Merge pull request #8847 from takaishi/support-keyboard-interactive
56045619d Merge pull request #8877 from paulcichonski/remote-esxi-bastion
698f74478 Merge pull request #8887 from hashicorp/untangle_ssh_docs_from_aws
aeedc9af7 Merge pull request #8879 from mbrancato/specify_keyvault_sku
5365fda5f Merge pull request #8884 from hashicorp/fix_codecov_config
4bd7b1409 Merge pull request #8732 from jhawk28/reorder_cdrom_drive
072a71b41 Merge pull request #8863 from hashicorp/update_go-cty_regex
8a1caaa80 Merge pull request #8837 from hashicorp/fix_8730
7873cabf6 Merge pull request #8858 from hashicorp/fix_8791
7e382d0df Merge pull request #8828 from mvitaly/fix_8816
8832b3e2c Merge pull request #8787 from jhawk28/vsphere_iso_multiple_disks
528174027 Merge pull request #8831 from rjhornsby/master
e35a87241 Merge pull request #8830 from hashicorp/d-var-file-hcl2-not-yet
```

After change
```
⇶  git log v1.5.4...v1.5.5 --first-parent --oneline --grep="Merge pull request #[0-9]\+" --grep="(#[0-9]\+)$"
413e19b84 Merge pull request #8942 from desolatorxxl/google-fix-ssh-keys-metadata
c387dc2c5 builder/vsphere-clone: Find the vm within the folder (#8938)
b17b211aa Add cleanup_remote_cache config option to vmware-iso (#8917)
e6368b924 Fix azure winrm_password attribution and allow to set winrm_username (#8928)
fcf10e9b7 Replace Amazon with Outscale for OSC BSU doc (#8944)
9240fb7f0 Fix typo in title (#8943)
2c6f0968b Allow accepting image for the members in OpenStack builder (#8931)
b81800db2 Merge pull request #8935 from zaventh/feature/start-on-boot
daffd9c31 CONTRIBUTING: Update documentation for linting on Travis (#8933)
3a9d356c9 golangci-lint: Update --new-from-rev option to check only newly added commits (#8923)
97d797d2f Fix small typos in osc-bsuvolume.html.md (#8926)
94863168b Merge pull request #8922 from hashicorp/f-vsphere_iso-export-ovf-options
56aebbeda Merge pull request #8920 from rhencke/patch-1
99b0b9831 Add ovf export capability to vsphere builders (#8764)
d068430ab make sure locals are evaluated only once variables are + test this (#8918)
ad8dafa3b HCL: add tests and fixes around var-file and var args  (#8914)
7979ab054 Add after_n_builds to codecov.yml (#8913)
3dae5df6e Merge pull request #8905 from hashicorp/fix_8493
811a7304a Merge pull request #8907 from hashicorp/fix_8428
fa49d2145 Merge pull request #8906 from hashicorp/fix_8904
b94937c05 Update provisioner_test.go (#8900)
2319521aa Add iso config test for checksum from file specific case (#8897)
23f56036a Merge pull request #8889 from hashicorp/hcl2_singular_blocks
dc9259f73 Merge pull request #8892 from zaventh/feature/vga-adapter
690bf714c Add Codecov badge and remove report style (#8896)
fc35f0200 Merge pull request #8890 from hashicorp/fix_8880
7972ab723 Merge pull request #8735 from hashicorp/fix_plugin_loading
890d7b2ec Merge pull request #8875 from hashicorp/fix_8812
e94ff7019 Merge pull request #8883 from hashicorp/fix_8835
```

scripts/prepare_changelog.sh

@@ -30,7 +30,7 @@ fi
 
 get_prs(){
     # git log v0.10.2...c3861d167533fb797b0fae0c380806625712e5f7 |
-    git log HEAD...${LAST_RELEASE} --first-parent --oneline --grep="Merge pull request #[0-9]\+" --grep="\(#[0-9]\+\)$" |
+    git log HEAD...${LAST_RELEASE} --first-parent --oneline --grep="Merge pull request #[0-9]\+" --grep="(#[0-9]\+)$" |
     grep -o "#\([0-9]\+\)" | awk -F\# '{print $2}' | while read line
     do
         grep -q "GH-${line}" CHANGELOG.md