CONTRIBUTING.md in tiddle-1.7.0 vs CONTRIBUTING.md in tiddle-1.7.1

@@ -2,11 +2,10 @@
 
 1. Fork the repo.
 2. Run the tests:
 
   ```
-  appraisal install
-  rake
+  BUNDLE_GEMFILE=gemfiles/<PICK YOUR FAVOURITE>.gemfile rake
   ```
 3. Introduce your change. If it's a new feature then write a test for it as well.
 4. Make sure that tests are passing.
 5. Push to your fork and submit a pull request.