Travis: add OSX to the build matrix
Travis: add OSX to the build matrix

YaccConstructor/FStar,A-Manning/FStar,hoheinzollern/FStar,MallabaevAzamat/FStar,FStarLang/FStar,YaccConstructor/FStar,hoheinzollern/FStar,MallabaevAzamat/FStar,MallabaevAzamat/FStar,hoheinzollern/FStar,hoheinzollern/FStar,FStarLang/FStar,A-Manning/FStar,MallabaevAzamat/FStar,YaccConstructor/FStar,A-Manning/FStar,YaccConstructor/FStar,FStarLang/FStar