chore: surpress mvn logging during release (#352)

Author: akerekes

.kokoro/release.sh

@@ -66,7 +66,7 @@ echo "pwd=$(pwd)"
 # Make sure `JAVA_HOME` is set and using jdk11.
 export JAVA_HOME=/usr/lib/jvm/java-1.11.0-openjdk-amd64
 echo "JAVA_HOME=$JAVA_HOME"
-mvn clean deploy -B \
+mvn clean deploy -B -q \
   -P sonatype-oss-release \
   --settings=../settings.xml \
   -Dgpg.executable=gpg \