Return Illuminate\Support\Fluent when possible, this allow developer to further chain additional command such as ->after() etc.

Signed-off-by: crynobone <crynobone@gmail.com>
Merge pull request #5172 from crynobone/feature/return-fluent

Schema blueprint return Illuminate\Support\Fluent when possible, this allow developer to further chain additional command such as ->after() etc.