Remove node15 until all peerDeps are up to date

Author: afontcu

.github/workflows/validate.yml

@@ -17,7 +17,7 @@ jobs:
   main:
     strategy:
       matrix:
-        node: [10.13, 12, 14, 15]
+        node: [10.13, 12, 14]
     runs-on: ubuntu-latest
     steps:
       - name: ⬇️ Checkout repo