Bring in es2017 lib

Author: Levertion

tsconfig.json

@@ -4,7 +4,7 @@
         "target": "es2017" /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', or 'ESNEXT'. */,
         "module": "commonjs" /* Specify module code generation: 'none', commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */,
         "lib": [
-            "es2015"
+            "es2017"
         ] /* Specify library files to be included in the compilation:  */,
         "outDir": "./out" /* Redirect output structure to the directory. */,
         "rootDir": "./src" /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */,