Update node-sass to 4.11.0 to support Node.js 11 (#12541)

## Description
Fixes #12539 by updating node-sass to support Node.js 11.

## How has this been tested?
Running `npm install` on macOS 10.14 with Node.js 11.2 without problems.

## Types of changes
Minor dependency bump to support Node.js 11.

## Checklist:
- [x] My code is tested.
- [x] My code follows the WordPress code style. <!-- Check code: `npm run lint`, Guidelines: https://make.wordpress.org/core/handbook/best-practices/coding-standards/javascript/ -->
- [x] My code follows the accessibility standards. <!-- Guidelines: https://make.wordpress.org/core/handbook/best-practices/coding-standards/accessibility-coding-standards/ -->
- [x] My code has proper inline documentation. <!-- Guidelines: https://make.wordpress.org/core/handbook/best-practices/inline-documentation-standards/javascript/ -->

package.json

@@ -90,7 +90,7 @@
 		"lint-staged": "7.2.0",
 		"lodash": "4.17.10",
 		"mkdirp": "0.5.1",
-		"node-sass": "4.9.2",
+		"node-sass": "4.11.0",
 		"path-type": "3.0.0",
 		"pegjs": "0.10.0",
 		"phpegjs": "1.0.0-beta7",