Upgrade typescript to 3.7.3 (#110)

Author: josephmbeveridge

template/package.json

@@ -23,7 +23,7 @@
     "jest": "^24.9.0",
     "metro-react-native-babel-preset": "^0.56.0",
     "react-test-renderer": "16.9.0",
-    "typescript": "^3.6.3"
+    "typescript": "^3.7.3"
   },
   "jest": {
     "preset": "react-native",