fix: update grunt-ts version

Author: Fatme

package.json

@@ -20,7 +20,7 @@
     "grunt-contrib-clean": "1.0.0",
     "grunt-contrib-watch": "0.6.1",
     "grunt-shell": "1.1.2",
-    "grunt-ts": "5.0.1",
+    "grunt-ts": "6.0.0-beta.16",
     "tns-core-modules": "5.1.2",
     "typescript": "2.9.2"
   },