Update to PostCSS@6

package.json

@@ -36,7 +36,7 @@
     "node": ">=4.2.1"
   },
   "dependencies": {
-    "autoprefixer": "^6.0.0",
+    "autoprefixer": "^7.0.0",
     "balanced-match": "^0.4.0",
     "chalk": "^1.1.1",
     "cosmiconfig": "^2.1.1",
@@ -57,19 +57,19 @@
     "micromatch": "^2.3.11",
     "normalize-selector": "^0.2.0",
     "pify": "^2.3.0",
-    "postcss": "^5.0.20",
+    "postcss": "^6.0.1",
     "postcss-less": "^0.14.0",
     "postcss-media-query-parser": "^0.2.0",
-    "postcss-reporter": "^3.0.0",
+    "postcss-reporter": "^4.0.0",
     "postcss-resolve-nested-selector": "^0.1.1",
-    "postcss-scss": "^0.4.0",
+    "postcss-scss": "^1.0.0",
     "postcss-selector-parser": "^2.1.1",
     "postcss-value-parser": "^3.1.1",
     "resolve-from": "^3.0.0",
     "specificity": "^0.3.0",
     "string-width": "^2.0.0",
     "style-search": "^0.1.0",
-    "sugarss": "^0.2.0",
+    "sugarss": "^1.0.0",
     "svg-tags": "^1.0.0",
     "table": "^4.0.1"
   },
@@ -88,8 +88,8 @@
     "jest": "^20.0.1",
     "npm-run-all": "^4.0.0",
     "npmpub": "^3.0.1",
-    "postcss-import": "^9.0.0",
-    "postcss-safe-parser": "^2.0.0",
+    "postcss-import": "^10.0.0",
+    "postcss-safe-parser": "^3.0.0",
     "remark-cli": "^3.0.0",
     "remark-preset-lint-consistent": "^2.0.0",
     "remark-preset-lint-recommended": "^2.0.0",