build: drop support old nodejs

Author: Scrum

.babelrc

@@ -4,7 +4,7 @@
       "@babel/preset-env",
       {
         "targets": {
-          "node": 8
+          "node": 10
         }
       }
     ],

package.json

@@ -13,7 +13,7 @@
   },
   "main": "lib/index.js",
   "engines": {
-    "node": ">=8"
+    "node": ">=10"
   },
   "scripts": {
     "version": "conventional-changelog -i changelog.md -s -r 0 && git add changelog.md",

readme.md

@@ -16,7 +16,7 @@ Adds the ability to use a custom property in the options, at-rules.
 $ npm install postcss-at-rules-variables
 ```
 
-> **Note:** This project is compatible with node v8+
+> **Note:** This project is compatible with node v10+
 
 ## Usage