[MNG-7441] Update version of loback (apache#708)

This issue is fluke, as logback is actually optional
dependency, but still, to cut reports like these from
root, let's do this update.

pom.xml

@@ -361,7 +361,7 @@ under the License.
       <dependency>
         <groupId>ch.qos.logback</groupId>
         <artifactId>logback-classic</artifactId>
-        <version>1.2.1</version>
+        <version>1.2.11</version>
         <optional>true</optional>
       </dependency>
       <!--  Wagon -->