Upgrade pitest-maven-plugin 1.7.5 -> 1.7.6 (#94)

See:
- https://github.com/hcoles/pitest/releases/tag/1.7.6
- hcoles/pitest@1.7.5...1.7.6

pom.xml

@@ -1147,7 +1147,7 @@
                 <plugin>
                     <groupId>org.pitest</groupId>
                     <artifactId>pitest-maven</artifactId>
-                    <version>1.7.5</version>
+                    <version>1.7.6</version>
                     <configuration>
                         <!-- Use multiple threads to speed things up. Extend
                         timeouts to prevent false positives as a result of