website: correct intro docs about terraform init -upgrade

"-upgrade" was misspelled as "-update".

website/docs/modules/usage.html.markdown

@@ -66,7 +66,7 @@ as well as performing other Terraform working directory initialization such
 as installing providers.
 
 By default the command will not check for available updates to already-installed
-modules, but you can use the `-update` option to check for available upgrades.
+modules, but you can use the `-upgrade` option to check for available upgrades.
 When version constraints are specified (as described in the following section)
 a newer version will be used only if it is within the given constraint.
 

website/intro/getting-started/modules.html.md

@@ -91,7 +91,7 @@ $ terraform init
 ```
 
 By default, this command does not check for new module versions that may be
-available, so it is safe to run multiple times. The `-update` option will
+available, so it is safe to run multiple times. The `-upgrade` option will
 additionally check for any newer versions of existing modules and providers
 that may be available.