Use Java 8 for publishing snapshots

To work around SSL problems, the build now uses Java 8 for the job that publishes snapshots to oss.sonatype.org.

Author: marcphilipp

.github/workflows/main.yml

@@ -48,7 +48,7 @@ jobs:
       - name: Set up JDK
         uses: actions/setup-java@v1
         with:
-          java-version: 6
+          java-version: 8
       - name: Publish snapshot artifacts
         env:
           OSSRH_USERNAME: ${{ secrets.OSSRH_USERNAME }}