Set gulp-protractor version back to 2.6.0

package.json

@@ -38,7 +38,7 @@
     "gulp-if": "~2.0.1",
     "gulp-inject": "~4.1.0",
     "gulp-minify-css": "~1.2.4",
-    "gulp-protractor": "~3.0.0",
+    "gulp-protractor": "~2.6.0",
     "gulp-rename": "~1.2.2",
     "gulp-replace": "~0.5.4",
     "gulp-rev-all": "~0.8.24",