Bump handlebars from 3.0.3 to 4.3.0

Bumps [handlebars](https://github.com/wycats/handlebars.js) from 3.0.3 to 4.3.0.
- [Release notes](https://github.com/wycats/handlebars.js/releases)
- [Changelog](https://github.com/handlebars-lang/handlebars.js/blob/master/release-notes.md)
- [Commits](handlebars-lang/handlebars.js@v3.0.3...v4.3.0)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

package-lock.json

@@ -20,7 +20,7 @@
     "browser-sync": "~2.18.12",
     "csswring": "~6.0.0",
     "es6-promise": "~4.1.0",
-    "handlebars": "~3.0.3",
+    "handlebars": "~4.3.0",
     "imagemin-pngquant": "~6.0.0",
     "jscs": "~1.13.1",
     "jshint": "~2.9.5",