Fix Synchronized.md documentation to use correct condition_variable::wait call
Fix Synchronized.md documentation to use correct condition_variable::wait call

Summary:
`condition_variable::wait_for` takes as second param `std::chrono::duration`
and not a predicate; what we want is `condition_variable::wait`.

Reviewed By: simpkins

Differential Revision: D4295305

fbshipit-source-id: 05f735fe6e7ecb9d8f42cb38a2985b9ce9dad984

facebook/folly,charsyam/folly,facebook/folly,rklabs/folly,facebook/folly,floxard/folly,rklabs/folly,Orvid/folly,rklabs/folly,Orvid/folly,rklabs/folly,Orvid/folly,charsyam/folly,facebook/folly,Orvid/folly,charsyam/folly,rklabs/folly,charsyam/folly,floxard/folly,Orvid/folly,floxard/folly,facebook/folly,floxard/folly,floxard/folly