Update supported nodejs versions

Drop node 10,12 support since these versions are EOL.
Add support for 18, 20.

https://nodejs.org/en/about/releases/

Author: tokuhirom

.github/workflows/test.yml

@@ -9,7 +9,8 @@ jobs:
 
     strategy:
       matrix:
-        node: [ '10', '12', '14', '16' ]
+        # https://nodejs.org/en/about/releases/
+        node: [ '14', '16', '18', '20' ]
       fail-fast: false
 
     name: Node.js ${{ matrix.node }}