Merge pull request #32 from TryGhost/renovate/gulp-5.x

Update dependency gulp to v5

Author: JohnONolan

package.json

@@ -48,7 +48,7 @@
     "beeper": "2.1.0",
     "cssnano": "5.1.15",
     "gscan": "5.2.4",
-    "gulp": "4.0.2",
+    "gulp": "5.0.1",
     "gulp-livereload": "4.0.2",
     "gulp-postcss": "10.0.0",
     "gulp-sourcemaps": "3.0.0",