💥 drop Node 4 support

mysticatea · mysticatea · commit 9557cbd96a04 · 2018-11-04T15:37:00.000+09:00
It has been EOL since April 2017.
devDependencies dropped it.
diff --git a/.travis.yml b/.travis.yml
@@ -2,7 +2,6 @@ sudo: false
 
 language: node_js
 node_js:
-  - "4"
   - "6"
   - "8"
   - "10"
diff --git a/package.json b/package.json
@@ -7,7 +7,7 @@
     "dist"
   ],
   "engines": {
-    "node": ">=4"
+    "node": ">=6"
   },
   "scripts": {
     "preversion": "npm test",
