Update go 1.5 references to 1.6

CHANGELOG.md

@@ -7,7 +7,7 @@ BACKWARDS INCOMPATIBILITIES:
     the packer-* plugin files** or packer will load out-of-date plugins from
     disk.
   * Release binaries are now provided via <https://releases.hashicorp.com>.
-  * Packer 0.9.0 is now built with Go 1.5. Future versions will drop support
+  * Packer 0.9.0 is now built with Go 1.6. Future versions will drop support
     for building with Go 1.4.
   * builder/amazon: Inline `user_data` for EC2 is now base64 encoded
     automatically [GH-2539]

CONTRIBUTING.md

@@ -53,8 +53,8 @@ it raises the chances we can quickly merge or address your contributions.
 If you have never worked with Go before, you will have to complete the
 following steps in order to be able to compile and test Packer.
 
-1. [Download](https://golang.org/dl) and install Go. Make sure your Go version
-   is at least Go 1.5. Packer _may_ work with older versions of Go but these
+1. [Download](https://golang.org/dl) and install Go. Go 1.6 or higher is
+   preferred. Packer _may_ work with versions of Go older than 1.5 but these
    are not supported.
 
 2. Set and export the `GOPATH` environment variable and update your `PATH`. For

Vagrantfile

@@ -3,7 +3,7 @@
 
 $script = <<SCRIPT
 # Fetch from https://golang.org/dl
-TARBALL="https://storage.googleapis.com/golang/go1.5.3.linux-amd64.tar.gz"
+TARBALL="https://storage.googleapis.com/golang/go1.6.linux-amd64.tar.gz"
 
 UNTARPATH="/opt"
 GOROOT="${UNTARPATH}/go"
@@ -20,7 +20,6 @@ sudo mkdir -p ${GOPATH}
 cat <<EOF >/tmp/gopath.sh
 export GOROOT="${GOROOT}"
 export GOPATH="${GOPATH}"
-export GO15VENDOREXPERIMENT="1"  # Not needed for Go 1.6 and up
 export PATH="${GOROOT}/bin:${GOPATH}/bin:\$PATH"
 EOF
 sudo mv /tmp/gopath.sh /etc/profile.d/gopath.sh