Merge pull request #291 from TongG/master

Fixed some typos.

doc/build-osx.md

@@ -13,8 +13,8 @@ built-in one is located in `/Applications/Utilities`.
 Preparation
 -----------
 
-You need to install XCode with all the options checked so that the compiler
-and everything is available in /usr not just /Developer. XCode should be
+You need to install Xcode with all the options checked so that the compiler
+and everything is available in /usr not just /Developer. Xcode should be
 available on your OS X installation media, but if not, you can get the
 current version from https://developer.apple.com/xcode/. If you install
 Xcode 4.3 or later, you'll need to install its command line tools. This can