Bump actions/upload-artifact from 1 to 2.3.1

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 1 to 2.3.1.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](https://github.com/actions/upload-artifact/compare/v1...v2.3.1)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/.github/workflows/maven.yml b/.github/workflows/maven.yml
index 8663340..0973027 100644
--- a/.github/workflows/maven.yml
+++ b/.github/workflows/maven.yml
@@ -29,7 +29,7 @@
     - name: Build with Maven
       run: mvn -B package --file pom.xml
     - name: Upload Maven build artifact
-      uses: actions/upload-artifact@v1
+      uses: actions/upload-artifact@v2.3.1
       with:
         name: asf-gitpubsub-jenkins.hpi
         path: target/asf-gitpubsub-jenkins.hpi