Using violationRules

I saw [here](https://stackoverflow.com/a/43018683/517193) that we can use `validationRules` with jacoco, but I've tried using it in the plugin without success:
```
android {
jacocoAndroidUnitTestReport {
violationRules {
rule {
limit {
minimum = 0.7
}
}
}
}
}
```
which gives the error
```
> Could not find method violationRules() for arguments [build_ei8l6elxe4xbtshycn6lr515j$_run_closure2$_closure12$_closure19@40e7e9ea] on object of type com.dicedmelon.gradle.jacoco.android.JacocoAndroidUnitTestReportExtension.
```