Add rubocop-bundle-safe executable

Within a bundled project, rubocop is executed via "bundle exec", while
outside of a project it's run executed directly.

bin/rubocop-bundle-safe

@@ -0,0 +1,7 @@
+#! /usr/bin/env bash
+
+if bundle check &>/dev/null; then
+  exec bundle exec rubocop "$@"
+else
+  exec rubocop "$@"
+fi