chore: update minimum java version to java 8 (#1281)

.github/.OwlBot.lock.yaml

@@ -1,3 +1,3 @@
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-java:latest
-  digest: sha256:204b7af96e6d481f19b0ff377aa379d46bc56dd06e1cc7c523f361dd9cbfeeaa
+  digest: sha256:a744afda1956beb7bd6dc8d0b740a7839bbe402e34e2f4ef24589074db53ceb0

.github/workflows/ci.yaml

@@ -53,7 +53,7 @@ jobs:
     - uses: actions/setup-java@v2
       with:
         distribution: zulu
-        java-version: 8
+        java-version: 11
     - run: java -version
     - run: .kokoro/build.sh
       env:

README.md

@@ -85,7 +85,7 @@ Cloud Domains uses gRPC for the transport layer.
 
 ## Supported Java Versions
 
-Java 7 or above is required for using this client.
+Java 8 or above is required for using this client.
 
 Google's Java client libraries,
 [Google Cloud Client Libraries][cloudlibs]
@@ -157,7 +157,6 @@ Apache 2.0 - See [LICENSE][license] for more information.
 
 Java Version | Status
 ------------ | ------
-Java 7 | [![Kokoro CI][kokoro-badge-image-1]][kokoro-badge-link-1]
 Java 8 | [![Kokoro CI][kokoro-badge-image-2]][kokoro-badge-link-2]
 Java 8 OSX | [![Kokoro CI][kokoro-badge-image-3]][kokoro-badge-link-3]
 Java 8 Windows | [![Kokoro CI][kokoro-badge-image-4]][kokoro-badge-link-4]