fix: Add appraisal gemfiles to repository

The gemfiles generated by appraisal need to be committed for CI to work.
Only ignoring the .gemfile.lock files which are generated at runtime.

.gitignore

@@ -14,4 +14,4 @@
 /spec/dummy/tmp/
 tmp/
 /spec/dummy/node_modules/
-/gemfiles/
+/gemfiles/*.gemfile.lock