Add Config::setPointScaleFactor to JavaScript binding

Summary:
Needed for a project I'm working on to properly render on high dpi screens. I've manually tested against my project to confirm it works.
Closes https://github.com/facebook/yoga/pull/612

Differential Revision: D6413517

Pulled By: emilsjolander

fbshipit-source-id: c298d7f6b58dc45aaaede2bb995df8615911a4a9

javascript/sources/nbind.cc

@@ -47,6 +47,7 @@ NBIND_CLASS(Config)
     method(destroy);
 
     method(setExperimentalFeatureEnabled);
+    method(setPointScaleFactor);
 
     method(isExperimentalFeatureEnabled);
 }