bump okhttp to 3.12.1 (#2273)
bump okhttp to 3.12.1 (#2273)

Summary:
bump okhttp to the latest version, with many fixes and improvements.

use latest and improved version.

Everything will works as normal.
Pull Request resolved: https://github.com/facebook/fresco/pull/2273

Reviewed By: oprisnik

Differential Revision: D13750721

Pulled By: erikandre

fbshipit-source-id: cf653449a0d7ba122256c4e1f70ee0bfc9e1c5fd

facebook/fresco,facebook/fresco,facebook/fresco,facebook/fresco,facebook/fresco,facebook/fresco