Bump mock-fs from 4.11.0 to 4.12.0 (#2662)

Bumps [mock-fs](https://github.com/tschaub/mock-fs) from 4.11.0 to 4.12.0.
- [Release notes](https://github.com/tschaub/mock-fs/releases)
- [Changelog](https://github.com/tschaub/mock-fs/blob/master/changelog.md)
- [Commits](tschaub/mock-fs@v4.11.0...v4.12.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Author: dependabot-preview[bot]

package-lock.json

@@ -61,7 +61,7 @@
     "mocha": "~5.2.0",
     "mocha-junit-reporter": "~1.23.3",
     "mocha-multi-reporters": "~1.1.7",
-    "mock-fs": "~4.11.0",
+    "mock-fs": "~4.12.0",
     "rewire": "~5.0.0",
     "sinon": "~9.0.2",
     "tslint": "~6.1.1",