Bump yarn from 1.15.2 to 1.22.0 in /css

Bumps [yarn](https://github.com/yarnpkg/yarn) from 1.15.2 to 1.22.0.
- [Release notes](https://github.com/yarnpkg/yarn/releases)
- [Changelog](https://github.com/yarnpkg/yarn/blob/master/CHANGELOG.md)
- [Commits](yarnpkg/yarn@v1.15.2...v1.22.0)

---
updated-dependencies:
- dependency-name: yarn
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

css/package.json

@@ -31,6 +31,6 @@
     "webpack": "^4.16.1",
     "webpack-cli": "^3.3.0",
     "webpack-merge": "^4.1.3",
-    "yarn": "^1.7.0"
+    "yarn": "^1.22.0"
   }
 }

css/yarn.lock

@@ -4343,7 +4343,7 @@ yargs@~1.2.6:
   dependencies:
     minimist "^0.1.0"
 
-yarn@^1.7.0:
-  version "1.15.2"
-  resolved "https://registry.npmjs.org/yarn/-/yarn-1.15.2.tgz"
-  integrity sha512-DhqaGe2FcYKduO42d2hByXk7y8k2k42H3uzYdWBMTvcNcgWKx7xCkJWsVAQikXvaEQN2GyJNrz8CboqUmaBRrw==
+yarn@^1.22.0:
+  version "1.22.0"
+  resolved "https://registry.yarnpkg.com/yarn/-/yarn-1.22.0.tgz#acf82906e36bcccd1ccab1cfb73b87509667c881"
+  integrity sha512-KMHP/Jq53jZKTY9iTUt3dIVl/be6UPs2INo96+BnZHLKxYNTfwMmlgHTaMWyGZoO74RI4AIFvnWhYrXq2USJkg==