Upgrade PostCSS to 6.0.1 (#834)

Author: termosa

package.json

@@ -34,7 +34,7 @@
     "js-beautify": "^1.6.3",
     "loader-utils": "^1.1.0",
     "lru-cache": "^4.0.1",
-    "postcss": "^5.0.21",
+    "postcss": "^6.0.1",
     "postcss-load-config": "^1.1.0",
     "postcss-selector-parser": "^2.0.0",
     "resolve": "^1.3.3",

yarn.lock

@@ -3152,7 +3152,15 @@ postcss-zindex@^2.0.1:
     postcss "^5.0.4"
     uniqs "^2.0.0"
 
-postcss@^5.0.10, postcss@^5.0.11, postcss@^5.0.12, postcss@^5.0.13, postcss@^5.0.14, postcss@^5.0.16, postcss@^5.0.2, postcss@^5.0.21, postcss@^5.0.4, postcss@^5.0.5, postcss@^5.0.6, postcss@^5.0.8, postcss@^5.2.16, postcss@^5.2.4:
+postcss@6.0.1:
+  version "6.0.1"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-6.0.1.tgz#000dbd1f8eef217aa368b9a212c5fc40b2a8f3f2"
+  dependencies:
+    chalk "^1.1.3"
+    source-map "^0.5.6"
+    supports-color "^3.2.3"
+
+postcss@^5.0.10, postcss@^5.0.11, postcss@^5.0.12, postcss@^5.0.13, postcss@^5.0.14, postcss@^5.0.16, postcss@^5.0.2, postcss@^5.0.4, postcss@^5.0.5, postcss@^5.0.6, postcss@^5.0.8, postcss@^5.2.16, postcss@^5.2.4:
   version "5.2.17"
   resolved "https://registry.yarnpkg.com/postcss/-/postcss-5.2.17.tgz#cf4f597b864d65c8a492b2eabe9d706c879c388b"
   dependencies:
@@ -3829,7 +3837,7 @@ sugarss@^0.2.0:
   dependencies:
     postcss "^5.2.4"
 
-supports-color@3.1.2:
+supports-color@3.1.2, supports-color@^3.1.0:
   version "3.1.2"
   resolved "https://registry.yarnpkg.com/supports-color/-/supports-color-3.1.2.tgz#72a262894d9d408b956ca05ff37b2ed8a6e2a2d5"
   dependencies:
@@ -3839,7 +3847,7 @@ supports-color@^2.0.0:
   version "2.0.0"
   resolved "https://registry.yarnpkg.com/supports-color/-/supports-color-2.0.0.tgz#535d045ce6b6363fa40117084629995e9df324c7"
 
-supports-color@^3.1.0, supports-color@^3.2.3:
+supports-color@^3.2.3:
   version "3.2.3"
   resolved "https://registry.yarnpkg.com/supports-color/-/supports-color-3.2.3.tgz#65ac0504b3954171d8a64946b2ae3cbb8a5f54f6"
   dependencies: