Build: Make the eslint:dev task not lint the dist/ folder

There was a mistake in paths logic that made the `dist/` folder linted
even in the `eslint:dev` task which is run before the build. Fix that by
explicitly ignoring the `dist/` folder at the end of the file list.

Closes gh-5257

Gruntfile.js

@@ -136,7 +136,11 @@ module.exports = function( grunt ) {
 						.map( filePath => filePath[ 0 ] === "!" ?
 							filePath.slice( 1 ) :
 							`!${ filePath }`
-						)
+						),
+
+					// Explicitly ignore `dist/` as it could be unignored by
+					// the above `.eslintignore` parsing.
+					"!dist/**/*.js"
 				]
 			}
 		},