revert: revert back to ts 2.5.3 because of angular/angular#21591

Author: Karthik K

packages/schematics/angular/application/files/package.json

@@ -45,6 +45,6 @@
     "protractor": "~5.1.2",
     "ts-node": "~4.1.0",
     "tslint": "~5.9.1",<% } %>
-    "typescript": "~2.6.2"
+    "typescript": "~2.5.3"
   }
 }