docs(contributing): fix NPM -> npm

Author: Awk34

Diff for: contributing.md

@@ -14,8 +14,8 @@ Additionally for this generator:
 To run the generator:
 1. Clone it and `cd` to its root
 2. `npm install`
-3. `npm link` (tells NPM to look to your own version)
-4. `yo angular-fullstack` as normal. It should run from your cloned version rather than the one downloaded from NPM.
+3. `npm link` (tells npm to look to your own version)
+4. `yo angular-fullstack` as normal. It should run from your cloned version rather than the one downloaded from npm.
 
 ## Git Commit Guidelines