build: update postcss to version 7.0.21

Author: renovate-bot

packages/angular_devkit/build_angular/package.json

@@ -39,7 +39,7 @@
     "minimatch": "3.0.4",
     "parse5": "4.0.0",
     "open": "7.0.0",
-    "postcss": "7.0.18",
+    "postcss": "7.0.21",
     "postcss-import": "12.0.1",
     "postcss-loader": "3.0.0",
     "raw-loader": "3.1.0",

yarn.lock

@@ -8191,7 +8191,16 @@ postcss-value-parser@^4.0.2:
   resolved "https://registry.yarnpkg.com/postcss-value-parser/-/postcss-value-parser-4.0.2.tgz#482282c09a42706d1fc9a069b73f44ec08391dc9"
   integrity sha512-LmeoohTpp/K4UiyQCwuGWlONxXamGzCMtFxLq4W1nZVGIQLYvMCJx3yAF9qyyuFpflABI9yVdtJAqbihOsCsJQ==
 
-postcss@7.0.18, postcss@^7.0.0, postcss@^7.0.1, postcss@^7.0.18, postcss@^7.0.2:
+postcss@7.0.21:
+  version "7.0.21"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-7.0.21.tgz#06bb07824c19c2021c5d056d5b10c35b989f7e17"
+  integrity sha512-uIFtJElxJo29QC753JzhidoAhvp/e/Exezkdhfmt8AymWT6/5B7W1WmponYWkHk2eg6sONyTch0A3nkMPun3SQ==
+  dependencies:
+    chalk "^2.4.2"
+    source-map "^0.6.1"
+    supports-color "^6.1.0"
+
+postcss@^7.0.0, postcss@^7.0.1, postcss@^7.0.18, postcss@^7.0.2:
   version "7.0.18"
   resolved "https://registry.yarnpkg.com/postcss/-/postcss-7.0.18.tgz#4b9cda95ae6c069c67a4d933029eddd4838ac233"
   integrity sha512-/7g1QXXgegpF+9GJj4iN7ChGF40sYuGYJ8WZu8DZWnmhQ/G36hfdk3q9LBJmoK+lZ+yzZ5KYpOoxq7LF1BxE8g==