SimpleWorkResult is deprecated in gradle 4.2

### Shadow Version
2.0.0, 2.0.1

### Gradle Version
4.2

### Expected Behavior
Clean build.

### Actual Behavior
Gradle prints a deprecation warning:
```
> Task :shadowJar
The SimpleWorkResult type has been deprecated and is scheduled to be removed in Gradle 5.0. Please use WorkResults.didWork() instead.
```