chore(deps): bump postcss from 7.0.17 to 7.0.39 in /website

Bumps [postcss](https://github.com/postcss/postcss) from 7.0.17 to 7.0.39.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/7.0.39/CHANGELOG.md)
- [Commits](postcss/postcss@7.0.17...7.0.39)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: indirect
...

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

website/yarn.lock

@@ -1772,7 +1772,7 @@ caw@^2.0.0, caw@^2.0.1:
     tunnel-agent "^0.6.0"
     url-to-options "^1.0.1"
 
-chalk@2.4.2, chalk@^2.0.0, chalk@^2.4.1, chalk@^2.4.2:
+chalk@2.4.2, chalk@^2.0.0, chalk@^2.4.1:
   version "2.4.2"
   resolved "https://registry.yarnpkg.com/chalk/-/chalk-2.4.2.tgz#cd42541677a54333cf541a49108c1432b44c9424"
   integrity sha512-Mti+f9lpJNcwF4tWV8/OrTTtF1gZi+f8FqlyAdouralcFWFQWF2+NgCHShjkCb+IFBLq9buZwE1xckQU4peSuQ==
@@ -5834,16 +5834,7 @@ postcss-value-parser@^4.1.0:
   resolved "https://registry.yarnpkg.com/postcss-value-parser/-/postcss-value-parser-4.2.0.tgz#723c09920836ba6d3e5af019f92bc0971c02e514"
   integrity sha512-1NNCs6uurfkVbeXG4S8JFT9t19m45ICnif8zWLd5oPSZ50QnwMfK+H3jv408d4jw/7Bttv5axS5IiHoLaVNHeQ==
 
-postcss@^7.0.0, postcss@^7.0.1, postcss@^7.0.5:
-  version "7.0.17"
-  resolved "https://registry.yarnpkg.com/postcss/-/postcss-7.0.17.tgz#4da1bdff5322d4a0acaab4d87f3e782436bad31f"
-  integrity sha512-546ZowA+KZ3OasvQZHsbuEpysvwTZNGJv9EfyCQdsIDltPSWHAeTQ5fQy/Npi2ZDtLI3zs7Ps/p6wThErhm9fQ==
-  dependencies:
-    chalk "^2.4.2"
-    source-map "^0.6.1"
-    supports-color "^6.1.0"
-
-postcss@^7.0.23, postcss@^7.0.32:
+postcss@^7.0.0, postcss@^7.0.1, postcss@^7.0.23, postcss@^7.0.32, postcss@^7.0.5:
   version "7.0.39"
   resolved "https://registry.yarnpkg.com/postcss/-/postcss-7.0.39.tgz#9624375d965630e2e1f2c02a935c82a59cb48309"
   integrity sha512-yioayjNbHn6z1/Bywyb2Y4s3yvDAeXGOyxqD+LnVOinq6Mdmd++SW2wUNVzavyyHxd6+DxzWGIuosg6P1Rj8uA==
@@ -6946,13 +6937,6 @@ supports-color@^5.3.0:
   dependencies:
     has-flag "^3.0.0"
 
-supports-color@^6.1.0:
-  version "6.1.0"
-  resolved "https://registry.yarnpkg.com/supports-color/-/supports-color-6.1.0.tgz#0764abc69c63d5ac842dd4867e8d025e880df8f3"
-  integrity sha512-qe1jfm1Mg7Nq/NSh6XE24gPXROEVsWHxC1LIx//XNlD9iw7YZQGjZNjYN7xGaEG6iKdA8EtNFW6R0gjnVXp+wQ==
-  dependencies:
-    has-flag "^3.0.0"
-
 supports-color@^7.1.0:
   version "7.2.0"
   resolved "https://registry.yarnpkg.com/supports-color/-/supports-color-7.2.0.tgz#1b7dcdcb32b8138801b3e478ba6a51caa89648da"