Fixes: Ancient version check matches unrelated gems

This commit will fix the following issue: #3188

It's done by fixing a regex, where a ```.``` was used, but the escaped version ```\.``` should be used.

## Content of $LOAD_PATH

    $LOAD_PATH.select { |e| e =~ %r'/bundler-' }
    
    # => 
    # [
    #   "/home/patrick/.rvm/gems/ruby-2.1.3@rails3/bundler/gems/bundler-010c47fd919a/lib",
    #   "/home/patrick/.rvm/gems/ruby-2.1.3@rails3/gems/bundler-1.7.6/lib"
    # ]

The line ```bundler-010c47fd919a/lib``` was matched with the old regex, but shout not be matched.