drop old node versions from CI on darwin. no longer supported by gith…

…ub actions (#71)

.github/workflows/main.yml

@@ -30,7 +30,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [10.x, 12.x, 14.x, 18.x, 20.x]
+        node-version: [18.x, 20.x]
 
     steps:
     - uses: actions/checkout@v2