Slim down test matrix to currently used versions

Also keeps 0.8 since we don't want to drop that support until 2.x

.travis.yml

@@ -1,16 +1,10 @@
 language: node_js
 node_js:
-  - "0.8"
+  - '6'
-  - "0.10"
+  - '4'
-  - "0.12"
+  - '0.12'
-  - "iojs-v1.8.4"
+  - '0.10'
-  - "iojs-v2.5.0"
+  - '0.8'
-  - "iojs-v3.3.0"
-  - "4"
-  - "5"
-matrix:
-  allow_failures:
-    - node_js: "5"
 addons:
   apt:
     sources: