Update contributing.md

Finish the sentence.

contributing.md

@@ -28,7 +28,7 @@ $ node bin/add-module collections is-awesome
 
 ## Running the tests
 
-You can either run *all* the tests for all the modules by doing `npm test` from the project root, this will include yours, or do it just for module by running `npm test` after `cd`'ing into your folder. If you're testing a single module you may need to run `npm install` in that specific module folder if you're missing dependencies. Just be sure to delete the 
+You can either run *all* the tests for all the modules by doing `npm test` from the project root, this will include yours, or do it just for module by running `npm test` after `cd`'ing into your folder. If you're testing a single module you may need to run `npm install` in that specific module folder if you're missing dependencies. Just be sure to delete the the `node_modules` folder that gets added.
 
 Don't worry about versioning or rebuilding the site, etc. That will be done when the pull request is merged.