Faiss 1.6.5

Fix version string in conda builds.

Summary: Currently, conda version strings are built from the latest git tag, which starts with the letter `v`. This confuses conda, which orders v1.6.5 before 1.6.3.

Reviewed By: LowikC

Differential Revision: D25151276

fbshipit-source-id: 7abfb547fee3468b26fedb6637a15e725755daf3