Fixed Query\Builder call to undefined method hasGetMutator when using lists method.

When using lists method in Query\Builder:
Call to undefined method Illuminate\Database\Query\Builder::hasGetMutator().
Need new method getMutatorMethod

Proposed changes fix issue.

Signed-off-by: Graham Campbell <graham@mineuk.com>
Fix test

replace hasGetMutator to getMutatorMethod

Signed-off-by: Graham Campbell <graham@mineuk.com>
Fixed a bc break due to the deletion of hasGetMutator

Signed-off-by: Graham Campbell <graham@mineuk.com>
Be consistent with types
Merge pull request #6688 from GrahamForks/4.2-mutators

[4.2] Mutator Fixes