dependency: bump pitest-maven from 1.6.7 to 1.6.8

Bumps [pitest-maven](https://github.com/hcoles/pitest) from 1.6.7 to 1.6.8.
- [Release notes](https://github.com/hcoles/pitest/releases)
- [Commits](hcoles/pitest@1.6.7...pitest-parent-1.6.8)

---
updated-dependencies:
- dependency-name: org.pitest:pitest-maven
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

pom.xml

@@ -214,7 +214,7 @@
     </maven.sevntu-checkstyle-check.checkstyle.version>
     <maven.versions.plugin.version>2.8.1</maven.versions.plugin.version>
     <java.version>1.8</java.version>
-    <pitest.plugin.version>1.6.7</pitest.plugin.version>
+    <pitest.plugin.version>1.6.8</pitest.plugin.version>
     <pitest.plugin.timeout.factor>10</pitest.plugin.timeout.factor>
     <pitest.plugin.timeout.constant>50000</pitest.plugin.timeout.constant>
     <pitest.plugin.threads>4</pitest.plugin.threads>