build: revert commit removing support for node v4

dpopp07 · dpopp07 · commit a367027da883 · 2018-11-07T19:25:38.000-06:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,6 +1,7 @@
 language: node_js
 sudo: false
 node_js:
+- 4
 - 6
 - 8
 before_install:
diff --git a/package.json b/package.json
@@ -98,7 +98,7 @@
     "websocket": "~1.0.26"
   },
   "engines": {
-    "node": ">=6"
+    "node": ">=4"
   },
   "scripts": {
     "precommit": "lint-staged",
