ci: drop node 8, adopt node 12 (#409)

BREAKING CHANGES: drop node 8

Author: anthony-redFox

.travis.yml

@@ -1,7 +1,7 @@
 language: node_js
 node_js:
-  - 8
   - 10
+  - 12
 
 services:
   - xvfb

package.json

@@ -58,7 +58,7 @@
     "sinon-chai": "^3.3.0"
   },
   "engines": {
-    "node": ">=8.0.0"
+    "node": ">=10.0.0"
   },
   "contributors": [
     "dignifiedquire <[email protected]>",