fix(tslint): get rid of warnings

package.json

@@ -123,8 +123,8 @@
     "@types/express": "4.0.35",
     "@types/fluent-ffmpeg": "0.0.2",
     "@types/mime": "0.0.29",
-    "@types/request": "0.0.42",
     "@types/node": "7.0.13",
+    "@types/request": "0.0.42",
     "@types/sinon": "2.1.2",
     "@types/ws": "0.0.39",
     "apiai": "4.0.2",
@@ -138,8 +138,8 @@
     "eslint-plugin-ava": "4.2.0",
     "finis": "0.0.2",
     "fluent-ffmpeg": "2.1.0",
-    "nyc": "10.2.0",
     "jsdoc-to-markdown": "^3.0.0",
+    "nyc": "10.2.0",
     "qrcode-terminal": "0.11.0",
     "request": "2.81.0",
     "shx": "0.2.2",

tsconfig.json

 {
   "compilerOptions": {
-    "target": "es2015"
+    "target": "es6"
     , "module": "commonjs"
     , "outDir": "dist"
     , "declaration": true