Travis config: disable node_modules caching

Stuff was passing until @isiahmeadows discovered that I had accidentally
removed uuid from devDependencies.  Seems Travis had just kept it in
cache, so it didn't catch my error.

I don't recall build times being outrageous without it, and this sort of
problems have happened before too, so I'm thinking this cache is more
trouble than it's worth.

Author: anko

.travis.yml

@@ -5,6 +5,3 @@ node_js:
   - "iojs"
   - "4"
   - "5.1"
-cache:
-  directories:
-    - node_modules