Update bower requirement to ^1.8.4

Updates the requirements on [bower](https://github.com/bower/bower) to permit the latest version.
- [Release notes](https://github.com/bower/bower/releases)
- [Changelog](https://github.com/bower/bower/blob/master/CHANGELOG.md)
- [Commits](https://github.com/bower/bower/commits/v1.8.4)

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

package.json

@@ -21,6 +21,6 @@
     "gulp-watch": "^4.3.6",
     "less-plugin-autoprefix": "^1.5.1",
     "less-plugin-clean-css": "^1.5.1",
-    "bower": "^1.8.0"
+    "bower": "^1.8.4"
   }
 }