[FIX] package.json: bump node version to v12

Node 10.x is no longer maintained, and since a recent commit [1],
a test fails with that version.

[1] 88fd1cf483

.github/workflows/deploy.yml

@@ -14,7 +14,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [10.x, 12.x, 14.x]
+        node-version: [12.x, 14.x]
 
     steps:
     - uses: actions/checkout@v2

package.json

@@ -10,7 +10,7 @@
     "dist"
   ],
   "engines": {
-    "node": ">=10.15.3"
+    "node": ">=12.18.3"
   },
   "scripts": {
     "build:bundle": "rollup -c",