chore: add Node.js 12 to ci services

Author: erisu

.travis.yml

@@ -1,10 +1,13 @@
 language: node_js
 sudo: false
 node_js:
-  - "6"
-  - "8"
-  - "10"
+  - 6
+  - 8
+  - 10
+  - 12
+
 install:
     - npm install
+
 script:
     - npm test

appveyor.yml

@@ -3,9 +3,10 @@
 
 environment:
   matrix:
-  - nodejs_version: "6"
-  - nodejs_version: "8"
-  - nodejs_version: "10"
+  - nodejs_version: 6
+  - nodejs_version: 8
+  - nodejs_version: 10
+  - nodejs_version: 12
 
 install:
   - ps: Install-Product node $env:nodejs_version