Allow override of bundler version or resolve from lock file

README.md

@@ -132,6 +132,9 @@ When set to `true`, previous version of the site will be restored before the Jek
 keep_files: [.git, hello.html]
 ```
 
+### bundler_version
+When set override the default bundler version provided.
+
 ## Use case: multi version publishing 
 
 Say you want to create a documentation website where you both have the current version (`v3.0`), but also `v1.0` and `v2.0`. You can then use a combination of `keep_history` and `target_path` along with the `actions/checkout@v2`action so that each version gets pushed in a separate folder without overwritting the previous one. 

action.yml

@@ -35,6 +35,9 @@ inputs:
       new dependencies. For example, use `apk --update add 
       imagemagick` to install ImageMagick.
     required: false
+  bundler_version:
+    description: 'When set override the default bundler version provided.'
+    required: false
 runs:
   using: 'docker'
   image: 'Dockerfile'

entrypoint.sh

@@ -8,6 +8,13 @@ if [ -n "$INPUT_PRE_BUILD_COMMANDS" ]; then
   eval "$INPUT_PRE_BUILD_COMMANDS"
 fi 
 
+echo "INPUT_BUNDLER_VERSON:${INPUT_BUNDLER_VERSON}"
+
+if [ -n "$INPUT_BUNDLER_VERSON" ]; then
+  echo "Installing bundler version specified by the user."
+  gem install bundler -v $INPUT_BUNDLER_VERSON
+fi 
+
 if [ -z "${INPUT_TOKEN}" ] && [ -n "${JEKYLL_PAT}" ]; then
   echo "::warning::The JEKYLL_PAT environment variable is deprecated. Please use the token parameter"
   INPUT_TOKEN=${JEKYLL_PAT}