Use Bundler 1 on Ruby 2.3

• At least until there is a new Bundler 2 release fixing rubygems/rubygems#3570.
• Fixes #51

Fix detection of head version when using ruby-version: debug

Fix checks for head versions

* Always use common.isHeadVersion().

Add support for ruby master debug builds

v1.33.0

Add support for ruby master debug builds

Update dependencies

v1.32.2

Update all dependencies

Fix release workflow bumping the v1 branch

• It needs a full checkout.

Add a working-directory input to resolve .ruby-version, Gemfile.lock, etc

See #50

Do not show a "Installing Bundler" group for bundler: none

v1.31.1

Document the consequences of using a specific version or commit sha

Use grouping in output and measure each group

• See MSP-Greg#3

Do no install Bundler on ruby-head/mingw/mswin

• Since latest Bundler is not necessarily compatible with ruby-head, and the stdlib Bundler should be recent enough for ruby-head
• See #48

Add latest CRuby release on Windows

• Fixes #46