Fix obsolete api waring [#260] issue to support android project

[KaelLuo]

No description provided.

[hal9002]

Can one of the admins review this PR?

[StefMa]

Is a task in the properties? Why not checking if this task is available via the Task Container?

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On Thu, Oct 10, 2019, 11:29 AM hal 9002 ***@***.***> wrote: Can one of the admins review this PR? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#296?email_source=notifications&email_token=ACOBQ67SMVDNQSCZRQT7TPLQN3YXHA5CNFSM4I7KIXJKYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOEA3SCHY#issuecomment-540483871>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACOBQ62C5C5S6QPQQG63SITQN3YXHANCNFSM4I7KIXJA> .

[KaelLuo]

Hey StefMa, thanks for the quick review.
variant is not a task, it's actually passed from "ReleasePlugin#attachArtifacts" function within this code

project.android.libraryVariants.all { variant ->
                String publicationName = variant.name
                MavenPublication publication = createPublication(publicationName, project, extension)
                new AndroidAttachments(publicationName, project, variant).attachTo(publication)
            }

In some other popular library, they also fix this kind of issue in same way, a similar fix discuss attached here:
google/protobuf-gradle-plugin#295

[mr-archano]

Thanks @KaelLuo for providing this. Just left a small remark.

[mr-archano]

I would prefer to extract a little method where to put this if statement (like we have already done in another plugin) so we can remove some duplication

[KaelLuo]

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