Bump watchify from 3.11.1 to 4.0.0

Bumps [watchify](https://github.com/browserify/watchify) from 3.11.1 to 4.0.0.
- [Release notes](https://github.com/browserify/watchify/releases)
- [Changelog](https://github.com/browserify/watchify/blob/master/CHANGELOG.md)
- [Commits](https://github.com/browserify/watchify/compare/v3.11.1...v4.0.0)

---
updated-dependencies:
- dependency-name: watchify
  dependency-type: direct:development
  update-type: version-update:semver-major
...
Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -93,7 +93,7 @@
     "tiny-emitter": "^2.0.2",
     "typescript": "^4.0.2",
     "vinyl": "^2.2.0",
-    "watchify": "^3.7.0",
+    "watchify": "^4.0.0",
     "wrap-text": "^1.0.7"
   },
   "browserslist": "chrome 57, edge 17, firefox 53, safari 10.1",