chore: lock typescript version

"typescript": "3.1.6"

Author: xidedix

package.json

@@ -64,6 +64,6 @@
     "tsickle": "^0.34.0",
     "tslib": "^1.9.3",
     "tslint": "~5.11.0",
-    "typescript": "^3.1.6"
+    "typescript": "3.1.6"
   }
 }