Fix #69 - Filter out 'ruby-' in .ruby-version file

Newer versions of Rails is pre-baked to have `ruby-x.x.x` in the `.ruby-version` file.

This breaks the legacy support as the whole contents of the file is used as the ruby version.

This PR adds a filtering when getting the legacy version from the file (remove `ruby-` prefix if it exists).

bin/get-version-from-legacy-file

@@ -4,9 +4,12 @@ get_legacy_version() {
   current_directory=$1
   ruby_version_file="$current_directory/.ruby-version"
 
-  # Get version from .ruby-version file. .ruby-version is used by rbenv and now rvm.
+  # Get version from .ruby-version file (filters out 'ruby-' prefix if it exists).
+  # The .ruby-version is used by rbenv and now rvm.
   if [ -f "$ruby_version_file" ]; then
-    cat "$ruby_version_file"
+    ruby_version=$(cat "$ruby_version_file")
+    ruby_prefix="ruby-"
+    echo ${ruby_version/#$ruby_prefix}
   fi
 }