Minor tweak to the wording of the vcpkg section
Minor tweak to the wording of the vcpkg section

Summary:
The commands as they were previously would attempt to install Folly as 32-bit, which would fail.
Also removes an extra `-` in the link's url.

Closes: https://github.com/facebook/folly/issues/713

Reviewed By: yfeldblum

Differential Revision: D6327981

fbshipit-source-id: ced8c86948b8be5c1dd88e14d6c3a77fc783aac9

Orvid/folly,facebook/folly,facebook/folly,rklabs/folly,facebook/folly,Orvid/folly,Orvid/folly,Orvid/folly,facebook/folly,facebook/folly,rklabs/folly,Orvid/folly,rklabs/folly,rklabs/folly,rklabs/folly