Target Node.js 6

.travis.yml

@@ -2,6 +2,5 @@ language: node_js
 node_js:
   - '8'
   - '6'
-  - '4'
 after_script:
   - './node_modules/.bin/nyc report --reporter=text-lcov > coverage.lcov && ./node_modules/.bin/codecov'

package.json

@@ -11,7 +11,7 @@
 	},
 	"main": "dist/index.js",
 	"engines": {
-		"node": ">=4"
+		"node": ">=6"
 	},
 	"scripts": {
 		"prerelease": "npm run build",

tsconfig.json

@@ -1,7 +1,7 @@
 {
 	"compilerOptions": {
 		"outDir": "dist",
-		"target": "es5",
+		"target": "es2015",
 		"lib": [
 			"es2015"
 		],