fix: update postcss to version ^7.0.0 (#1004)

Author: renovate[bot]

package.json

@@ -41,7 +41,7 @@
     "less": "^3.0.0",
     "node-sass": "^4.5.3",
     "node-sass-tilde-importer": "^1.0.0",
-    "postcss": "^6.0.2",
+    "postcss": "^7.0.0",
     "postcss-url": "^7.3.0",
     "read-pkg-up": "^4.0.0",
     "rimraf": "^2.6.1",

yarn.lock

@@ -867,6 +867,14 @@ chalk@^2.0.1, chalk@^2.3.0, chalk@^2.3.1, chalk@^2.3.2:
     escape-string-regexp "^1.0.5"
     supports-color "^5.3.0"
 
+chalk@^2.4.1:
+  version "2.4.1"
+  resolved "https://registry.yarnpkg.com/chalk/-/chalk-2.4.1.tgz#18c49ab16a037b6eb0152cc83e3471338215b66e"
+  dependencies:
+    ansi-styles "^3.2.1"
+    escape-string-regexp "^1.0.5"
+    supports-color "^5.3.0"
+
 check-error@^1.0.1:
   version "1.0.2"
   resolved "https://registry.yarnpkg.com/check-error/-/check-error-1.0.2.tgz#574d312edd88bb5dd8912e9286dd6c0aed4aac82"
@@ -3519,14 +3527,22 @@ postcss-value-parser@^3.2.3:
   version "3.3.0"
   resolved "https://registry.yarnpkg.com/postcss-value-parser/-/postcss-value-parser-3.3.0.tgz#87f38f9f18f774a4ab4c8a232f5c5ce8872a9d15"
 
-postcss@^6.0.1, postcss@^6.0.2, postcss@^6.0.20:
+postcss@^6.0.1, postcss@^6.0.20:
   version "6.0.21"
   resolved "https://registry.yarnpkg.com/postcss/-/postcss-6.0.21.tgz#8265662694eddf9e9a5960db6da33c39e4cd069d"
   dependencies:
     chalk "^2.3.2"
     source-map "^0.6.1"
     supports-color "^5.3.0"
 
+postcss@^7.0.0:
+  version "7.0.0"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-7.0.0.tgz#163f70d2fe2715c6d4a4b3d300051c1ea9594aa9"
+  dependencies:
+    chalk "^2.4.1"
+    source-map "^0.6.1"
+    supports-color "^5.4.0"
+
 prepend-http@^1.0.1:
   version "1.0.4"
   resolved "https://registry.yarnpkg.com/prepend-http/-/prepend-http-1.0.4.tgz#d4f4562b0ce3696e41ac52d0e002e57a635dc6dc"