chore: update typescript version for source

Author: Elena Hristova

src/package.json

@@ -48,7 +48,7 @@
     "devDependencies": {
         "tns-core-modules": "^5.0.0",
         "tns-platform-declarations": "^5.0.0",
-        "typescript": "~3.1.6",
+        "typescript": "~3.4.5",
         "tslint": "~5.11.0"
     },
     "dependencies": {