[rubygems/rubygems] Use shellsplit instead of array of strings

Previously, the command string to be used for the shell command
was first generated and then split using shellsplit. This change
reverts the current behavior as it breaks if the value of remote
contains a space.

rubygems/rubygems@6649ee10b0

lib/bundler/gem_helper.rb

@@ -129,8 +129,8 @@ def built_gem_path
 
     def git_push(remote = nil)
       remote ||= default_remote
-      sh(%W[git push #{remote} refs/heads/#{current_branch}])
-      sh(%W[git push #{remote} refs/tags/#{version_tag}])
+      sh("git push #{remote} refs/heads/#{current_branch}".shellsplit)
+      sh("git push #{remote} refs/tags/#{version_tag}".shellsplit)
       Bundler.ui.confirm "Pushed git commits and release tag."
     end