Fix incorrect error message on Windows

We're parsing the exception message here looking for a path, but we were
not considering potential drive letters on Windows.

bundler/lib/bundler/source/git/git_proxy.rb

@@ -118,7 +118,7 @@ def copy_to(destination, submodules = false)
               git_retry %(clone --no-checkout --quiet "#{path}" "#{destination}")
               File.chmod(((File.stat(destination).mode | 0o777) & ~File.umask), destination)
             rescue Errno::EEXIST => e
-              file_path = e.message[%r{.*?(/.*)}, 1]
+              file_path = e.message[%r{.*?((?:[a-zA-Z]:)?/.*)}, 1]
               raise GitError, "Bundler could not install a gem because it needs to " \
                 "create a directory, but a file exists - #{file_path}. Please delete " \
                 "this file and try again."

bundler/spec/install/gemfile/git_spec.rb

@@ -933,8 +933,6 @@
   end
 
   it "prints a friendly error if a file blocks the git repo" do
-    skip "drive letter is not detected correctly in error message" if Gem.win_platform?
-
     build_git "foo"
 
     FileUtils.mkdir_p(default_bundle_path)