Set TypeScript compile target to ECMAScript ES2017.

.travis.yml

@@ -1,10 +1,10 @@
 language: node_js
 node_js:
- - "6"
  - "8"
  - "9"
  - "10"
  - "11"
+ - "12"
 install:
 - yarn install
 script:

README.md

@@ -66,7 +66,8 @@ Support for encoding / format details:
 
 ## Compatibility
 
-The JavaScript in runtime is compliant with [ECMAScript 2015 (ES6)](https://nodejs.org/en/docs/es6/).
+The JavaScript in runtime is compliant with [ECMAScript 2017 (ES8)](https://en.wikipedia.org/wiki/ECMAScript#8th_Edition_-_ECMAScript_2017).
+Requires [Node.js®](https://nodejs.org/) version 6 or higher.
 
 ### Browser Support
 

package.json

@@ -108,7 +108,7 @@
     ]
   },
   "engines": {
-    "node": "*"
+    "node": ">=8"
   },
   "repository": {
     "type": "git",

tsconfig.json

@@ -3,7 +3,7 @@
     "inlineSources": false,
     "module": "commonjs",
     "moduleResolution": "node",
-    "target": "es6"
+    "target": "ES2017"
   }
 }