deps: update dependency ch.qos.logback:logback-classic to v1.2.8 (#610)

Fixes [CVE-2021-4104](https://access.redhat.com/security/cve/CVE-2021-4104)

Author: renovate-bot

pom.xml

@@ -14,7 +14,7 @@
   </description>
 
   <properties>
-    <logback.version>1.2.7</logback.version>
+    <logback.version>1.2.8</logback.version>
     <easymock.version>3.6</easymock.version>
     <truth.version>1.1.3</truth.version>
     <logging.version>3.5.1</logging.version>