Maven release v1.8.0 (#2152)

* [Gradle Release Plugin] - pre tag commit:  'v1.8.0-maven'.

* [Gradle Release Plugin] - new version commit:  'v1.8.1-SNAPSHOT-maven'.

Author: chanseokoh

jib-maven-plugin/gradle.properties

@@ -1 +1 @@
-version = 1.7.1-SNAPSHOT
+version = 1.8.1-SNAPSHOT