Drop Node 10 support

Increase minimum Node version to 12.  Node 10 reached end-of-life on
April 30, 2021.

Author: wimpyprogrammer

.github/workflows/tests.yml

@@ -18,7 +18,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        node-version: [10.x, 14.x]
+        node-version: [12.x, 14.x]
 
     steps:
       - name: Checkout repository

package.json

@@ -18,7 +18,7 @@
   ],
   "sideEffects": false,
   "engines": {
-    "node": ">=10"
+    "node": ">=12"
   },
   "scripts": {
     "build": "run-s clean build:*",