Update min node version to 4. 0.12 is no longer supported.

Author: ChadKillingsworth

.travis.yml

@@ -2,7 +2,7 @@ language: node_js
 node_js:
 - '7'
 - '6'
-- '0.12'
+- '4'
 branches:
   only:
   - master

package.json

@@ -56,6 +56,6 @@
     "pretest": "./build_compiler.js"
   },
   "engines": {
-    "node": ">=0.12.0"
+    "node": ">=4"
   }
 }