Replace deprecated set-env command.

Author: mrstegeman

.github/workflows/release.yml

@@ -13,8 +13,8 @@ jobs:
       - uses: actions/setup-node@v1
         with:
           node-version: 8
-      - name: Set env
-        run: echo ::set-env name=RELEASE_VERSION::$(echo ${GITHUB_REF:11})
+      - name: Set release version
+        run: echo "RELEASE_VERSION=${GITHUB_REF:11}" >> $GITHUB_ENV
       - name: Package project
         run: |
           ./package.sh