Fix windows release (#62)

**Issue:**
The windows release workflow breaks, due to manual install of latest bundler, which no longer works with Ruby 2.x

**Description of changes:**
Remove manual install of bundler, the `setup-ruby` action already takes care of installing a compatible version

builder.json

@@ -3,7 +3,6 @@
     "packages": [],
     "build_steps": [
         "ruby -v",
-        "command -v bundler >/dev/null 2>&1 || gem install bundler",
         "bundle install",
         "bundle exec rake release"
     ]