Replace gulp with npm scripts (#7402)

Gulp removed from toolchain in favour of simpler build process

.github/workflows/ci.yml

@@ -28,9 +28,6 @@ jobs:
         Xvfb :99 -screen 0 1024x768x24 &
         echo "::set-env name=DISPLAY:::99.0"
       if: runner.os == 'Linux'
-    - name: Install gulp
-      run: npm install --global gulp
-      if: runner.os == 'macOS'
     - name: Install chrome
       run: |
         brew update
@@ -45,13 +42,13 @@ jobs:
     - name: Build and Test
       run: |
         npm install
-        gulp build
-        gulp test --coverage ${BROWSERS}
+        npm run build
+        npm test
     - name: Package
       run: |
         npm run docs
         npm run typedoc
-        gulp package
+        npm pack
     - name: Publish Test Results
       run: cat ./coverage/lcov.info | ./node_modules/.bin/coveralls
       shell: bash