Release v0.120.0 (#6988)

Author: kolea2

google-cloud-contrib/google-cloud-logging-logback/pom.xml

@@ -20,7 +20,7 @@
   <parent>
     <groupId>com.google.cloud</groupId>
     <artifactId>google-cloud-contrib</artifactId>
-    <version>0.119.1-alpha-SNAPSHOT</version><!-- {x-version-update:google-cloud-contrib:current} -->
+    <version>0.120.0-alpha</version><!-- {x-version-update:google-cloud-contrib:current} -->
   </parent>
   <dependencies>
     <dependency>