Merge pull request #14113 from Microsoft/vladima/update-gulp-ts

update gulp-typescript to 3.1.5

package.json

@@ -60,7 +60,7 @@
         "gulp-insert": "latest",
         "gulp-newer": "latest",
         "gulp-sourcemaps": "latest",
-        "gulp-typescript": "3.1.3",
+        "gulp-typescript": "3.1.5",
         "into-stream": "latest",
         "istanbul": "latest",
         "jake": "latest",