deps: update logback.version to v1.2.6 (#528)

[![WhiteSource Renovate](https://app.renovatebot.com/images/banner.svg)](https://renovatebot.com)

This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [ch.qos.logback:logback-core](http://logback.qos.ch) ([source](https://github.com/ceki/logback)) | `1.2.5` -> `1.2.6` | [![age](https://badges.renovateapi.com/packages/maven/ch.qos.logback:logback-core/1.2.6/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/ch.qos.logback:logback-core/1.2.6/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/ch.qos.logback:logback-core/1.2.6/compatibility-slim/1.2.5)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/ch.qos.logback:logback-core/1.2.6/confidence-slim/1.2.5)](https://docs.renovatebot.com/merge-confidence/) |
| [ch.qos.logback:logback-classic](http://logback.qos.ch) ([source](https://github.com/ceki/logback)) | `1.2.5` -> `1.2.6` | [![age](https://badges.renovateapi.com/packages/maven/ch.qos.logback:logback-classic/1.2.6/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/ch.qos.logback:logback-classic/1.2.6/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/ch.qos.logback:logback-classic/1.2.6/compatibility-slim/1.2.5)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/ch.qos.logback:logback-classic/1.2.6/confidence-slim/1.2.5)](https://docs.renovatebot.com/merge-confidence/) |

---

### Configuration

📅 **Schedule**: At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about these updates again.

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box.

---

This PR has been generated by [WhiteSource Renovate](https://renovate.whitesourcesoftware.com). View repository job log [here](https://app.renovatebot.com/dashboard#github/googleapis/java-logging-logback).

Author: renovate-bot

pom.xml

@@ -14,7 +14,7 @@
   </description>
 
   <properties>
-    <logback.version>1.2.5</logback.version>
+    <logback.version>1.2.6</logback.version>
     <easymock.version>3.6</easymock.version>
     <truth.version>1.1.3</truth.version>
     <logging.version>3.1.1</logging.version>