Update dependency gulp-eslint to v6

Author: renovate-bot

tasks/package.json

@@ -49,7 +49,7 @@
     "gulp-concat": "2.6.1",
     "gulp-csscomb": "3.0.8",
     "gulp-env": "0.4.0",
-    "gulp-eslint": "5.0.0",
+    "gulp-eslint": "6.0.0",
     "gulp-header": "2.0.7",
     "gulp-load-plugins": "1.5.0",
     "gulp-mocha": "6.0.0",