brew.sh: tweak xcode hint to auto-accept license

Small improvement to the xcode license hint. Reduces friction by allowing user to accept the license in a single step. 
Reference: http://apple.stackexchange.com/questions/175069/how-to-accept-xcode-license

Library/Homebrew/brew.sh

@@ -165,7 +165,7 @@ EOS
     then
       odie <<EOS
 You have not agreed to the Xcode license. Please resolve this by running:
-  sudo xcodebuild -license
+  sudo xcodebuild -license accept
 EOS
     fi
   fi