Bump version to 2.4.0
Bump version to 2.4.0

Reviewed By: wizh

Differential Revision: D25995126

fbshipit-source-id: 77fc8dedc5b5f15c5d76045d1b8852ab751a022a

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