Bump postcss from 7.0.34 to 7.0.39 in /server/frontend

Bumps [postcss](https://github.com/postcss/postcss) from 7.0.34 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](https://github.com/postcss/postcss/compare/7.0.34...7.0.39)

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

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

server/frontend/package-lock.json

@@ -2568,6 +2568,11 @@
         "sha.js": "^2.4.8"
       }
     },
+    "picocolors": {
+      "version": "0.2.1",
+      "resolved": "https://registry.npmjs.org/picocolors/-/picocolors-0.2.1.tgz",
+      "integrity": "sha512-cMlDqaLEqfSaW8Z7N5Jw+lyIW869EzT73/F5lhtY9cLGoVxSXznfgfXMO0Z5K0o0Q2TkTXq+0KFsdnSe3jDViA=="
+    },
     "picomatch": {
       "version": "2.0.7",
       "resolved": "https://registry.npmjs.org/picomatch/-/picomatch-2.0.7.tgz",
@@ -2592,13 +2597,12 @@
       "integrity": "sha1-AerA/jta9xoqbAL+q7jB/vfgDqs="
     },
     "postcss": {
-      "version": "7.0.34",
-      "resolved": "https://registry.npmjs.org/postcss/-/postcss-7.0.34.tgz",
-      "integrity": "sha512-H/7V2VeNScX9KE83GDrDZNiGT1m2H+UTnlinIzhjlLX9hfMUn1mHNnGeX81a1c8JSBdBvqk7c2ZOG6ZPn5itGw==",
+      "version": "7.0.39",
+      "resolved": "https://registry.npmjs.org/postcss/-/postcss-7.0.39.tgz",
+      "integrity": "sha512-yioayjNbHn6z1/Bywyb2Y4s3yvDAeXGOyxqD+LnVOinq6Mdmd++SW2wUNVzavyyHxd6+DxzWGIuosg6P1Rj8uA==",
       "requires": {
-        "chalk": "^2.4.2",
-        "source-map": "^0.6.1",
-        "supports-color": "^6.1.0"
+        "picocolors": "^0.2.1",
+        "source-map": "^0.6.1"
       }
     },
     "postcss-modules-extract-imports": {