change group id in showcase

Author: JoeWang1127

java-showcase/gapic-showcase/pom.xml

@@ -294,7 +294,7 @@
           <scope>test</scope>
         </dependency>
         <dependency>
-          <groupId>com.google.api</groupId>
+          <groupId>com.google.cloud</groupId>
           <artifactId>logback-extension</artifactId>
           <version>0.1.0-SNAPSHOT</version>
           <scope>test</scope>