Update BUILD.md
Update BUILD.md

Replace all instances of XCode with Xcode.
Xetlin/Lua,fodinabor/Polycode,fodinabor/Polycode,GovanifY/Polycode,mcanthony/Polycode,hksonngan/Polycode,zeebok/Polycode,carlosmarti/Polycode,thorsummoner/polycode,carlosmarti/Polycode,GovanifY/Polycode,fodinabor/Polycode,hksonngan/Polycode,thorsummoner/polycode,zeebok/Polycode,GovanifY/Polycode,cartman300/Polycode,thorsummoner/polycode,Xetlin/Lua,GovanifY/Polycode,sshaileshk/Polycode,ivansafrin/Polycode,cartman300/Polycode,cartman300/Polycode,hksonngan/Polycode,mcanthony/Polycode,thorsummoner/polycode,mcanthony/Polycode,mcanthony/Polycode,zeebok/Polycode,zeebok/Polycode,Xetlin/Lua,sshaileshk/Polycode,ivansafrin/Polycode,cartman300/Polycode,fodinabor/Polycode,ivansafrin/Polycode,sshaileshk/Polycode,ivansafrin/Polycode,Xetlin/Lua,sshaileshk/Polycode,carlosmarti/Polycode,hksonngan/Polycode