chore: update node versions

.travis.yml

@@ -1,8 +1,7 @@
 language: node_js
 node_js:
-  - "8.0"
-  - "7.2"
-  - "6.11"
+  - "8"
+  - "6"
 install:
   - yarn install
   - yarn run build

appveyor.yml

@@ -1,6 +1,8 @@
 # Test against the latest version of this Node.js version
 environment:
-  nodejs_version: "6"
+  matrix:
+    - nodejs_version: "6"
+    - nodejs_version: "8"
 
 # Install scripts. (runs after repo cloning)
 install:

package.json

@@ -62,8 +62,8 @@
     "postinstall": "opencollective postinstall || exit 0"
   },
   "engines": {
-    "node": ">=4.3.0 <5.0.0 || >=5.10",
-    "npm": ">=3.0.0"
+    "node": ">=6.11",
+    "npm": ">=3.10.0"
   },
   "dependencies": {
     "@nuxtjs/youch": "3.0.1",