Use PostCSS 6x

- Also, update dev dependencies

Author: jonathantneal

package.json

@@ -17,12 +17,12 @@
   },
   "homepage": "https://github.com/MattDiMu/postcss-replace-overflow-wrap",
   "dependencies": {
-    "postcss": "^5.0.16"
+    "postcss": "^6.0.1"
   },
   "devDependencies": {
-    "ava": "^0.14.0",
-    "eslint": "^2.1.0",
-    "eslint-config-postcss": "^2.0.0"
+    "ava": "^0.19.1",
+    "eslint": "^3.19.0",
+    "eslint-config-postcss": "^2.0.2"
   },
   "scripts": {
     "test": "ava && eslint *.js"