Replace 12 spaces with newline in commit description

To avoid unexpected indentation like in:

```
Update Helm charts of prometheus

            Build-Url: https://ci.mcp.mirantis.net/job/helm-publish-metadata-prometheus/80/
Related-To: PRODX-8030

Change-Id: I2e9a3899c195ed2f5d4543adc08f7650a10e0953
```

Change-Id: I4dca3109182cfb7ac60eb079e90c2c1312089d65
diff --git a/src/com/mirantis/mk/ReleaseWorkflow.groovy b/src/com/mirantis/mk/ReleaseWorkflow.groovy
index a531d48..da17fb9 100644
--- a/src/com/mirantis/mk/ReleaseWorkflow.groovy
+++ b/src/com/mirantis/mk/ReleaseWorkflow.groovy
@@ -181,8 +181,7 @@
         commitMessage =
                 """${comment}
 
-               |${ChangeId}
-            """.stripMargin()
+               |${ChangeId}\n""".stripMargin()
 
         // Add some useful info (if it present) to commit message
         if (env.BUILD_URL) {