Drop Node.js 8.x support.

It's EOL and shouldn't be used in production anymore.

Also add Node.js 13 in CI.

Author: XhmikosR

.github/workflows/test.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        node: [8.16.1, 10, 12]
+        node: [10, 12, 13]
         os: [ubuntu-latest, windows-latest]
 
     steps:

package.json

@@ -38,7 +38,7 @@
     "xo": "^0.25.3"
   },
   "engines": {
-    "node": ">=8.10.0"
+    "node": ">=10"
   },
   "xo": {
     "space": 4,