Methods getLastPage() and getCurrentPage() should return integer

Atleast according to ArraySerializer::paginator() where both are
typecasted to integer.

https://github.com/thephpleague/fractal/blob/master/src/Serializer/ArraySerializer.php#L76
Merge pull request #112 from tuupola/pagination-string-to-integer

Methods getLastPage() and getCurrentPage() should return integer