fix showcase paths

Author: chingor13

sdk-platform-java/java-showcase/scripts/generate_showcase.sh

@@ -71,7 +71,7 @@ fi
 
 pushd sdk-platform-java
 GENERATOR_VERSION=$(mvn help:evaluate -Dexpression=project.version -q -DforceStdout -pl gapic-generator-java)
-popd sdk-platform-java
+popd
 
 echo "generating showcase"
 workspace_name="/workspace"