Using generateAssertionsInPackage in Maven results in compilation issues

#### Summary
Some classes for which I generate assertion classes contain methods with parameter types that are in the same package. If I then use `` to generate the assertion classes in a different package, they miss the required imports for these types.

#### Example

```java
public class Holder {
private Collection values;
}
```
```xml

org.assertj
assertj-assertions-generator-maven-plugin
2.1.0



generate-assertions




assertj.generated.assertions

```
Results in the following assertion class:
```java
public class HolderAssert extends AbstractHolderAssert {
(..)
}
```
```java
import org.assertj.core.api.AbstractObjectAssert;
import org.assertj.core.internal.Iterables;
import org.assertj.core.util.Objects;

public abstract class AbstractHolderAssert, A extends Holder> extends AbstractObjectAssert {

(..)

// class MyCustomClass not imported == compilation error -->
public S hasValues(MyCustomClass... values) {
(..)
}
}
```