build: update typescript to 3.1.6 (angular#12849)

* fix(@angular-devkit/build-optimizer): update typescript to 3.1.6

* build: update typescript to 3.1.6

Author: alan-agius4

package.json

@@ -35,7 +35,7 @@
   "devDependencies": {
     "@angular/compiler": "^7.0.0-rc.0",
     "@angular/compiler-cli": "^7.0.0-rc.0",
-    "typescript": "~3.1.5",
+    "typescript": "~3.1.6",
     "webpack": "^4.0.0"
   }
 }