Don't test Node 5 in CI

Node 5 is neither latest or LTS. This is not removing support for
Node 5, it's simpky removing it from day-to-day CI for faster builds.

.travis.yml

 language: node_js
 node_js:
   - "6"
-  - "5"
   - "4"
   - "0.12"
   - "0.10"

appveyor.yml

@@ -112,7 +112,6 @@
       - nodejs_version: 0.10
       - nodejs_version: 0.12
       - nodejs_version: 4
-      - nodejs_version: 5
       - nodejs_version: 6
 
   install: