feat: bump typescript target to ES2017 (#729)

Sets the TypeScript compile target to ES2017 as ES2015 is now 8 years
old. Furthermore, ES2017 targets do not transpile async/await to JS
generators, which means that stack traces will now be readable.

Author: hf

tsconfig.json

@@ -7,7 +7,7 @@
     "outDir": "dist/main",
     "rootDir": "src",
     "sourceMap": true,
-    "target": "ES2015",
+    "target": "ES2017",
 
     "strict": true,