Fix attach for pivot tables that only have either a created_at or updated_at timestamp.
Change explicit references to 'created_at' and 'updated_at' to 'createdAt' and 'updatedAt' method calls
Merge pull request #5748 from stidges/4.2-pivot-timestamps

[4.2] Eloquent BelongsToMany Pivot Timestamps
Merge branch '4.2'