Remove node 6 support

.travis.yml

@@ -4,11 +4,6 @@ node_js:
 - stable
 - 10
 - 8
-# 6.13 and 6.14 causing unreasonable errors in SymbolDefinition.initialize.
-# https://travis-ci.org/paperjs/paper.js/jobs/434854796
-# To avoid these versions, we specify version to 6.12 as temporary solution.
-# See https://github.com/paperjs/paper.js/issues/1523
-- 6.12
 sudo: false
 env:
   matrix:

package.json

@@ -33,7 +33,7 @@
     "README.md"
   ],
   "engines": {
-    "node": ">=4.0.0"
+    "node": ">=8.0.0"
   },
   "husky": {
     "hooks": {