feat: Add support for Node 16, 18 (#42)

BREAKING CHANGE: Removes support for Node 12, 15.

Author: mtrezza

.github/workflows/ci.yml

@@ -8,10 +8,10 @@ on:
       - '**'
 jobs:
   test:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
     strategy:
       matrix:
-        node: [ '12', '14', '15' ]
+        node: [ '14', '16', '18' ]
     timeout-minutes: 30
     env:
       COVERALLS_REPO_TOKEN: ${{ secrets.COVERALLS_REPO_TOKEN }}