message: Update the macOS version on the README
diff: @@ -21,11 +21,11 @@ top of the LLDB Debugger.
  To build LLDB for Swift, you must have the following prerequisites
  installed on your development system:
  -* OS X Requirements
  +* macOS Requirements
  - * OS X 10.11 (El Capitan) or later.
  + * macOS 10.12.6 or later.
  - * [Xcode 7.2 Beta 4][xcode-download] or later.
  + * [Xcode 9.2][xcode-download] or later.
  * [Cmake][cmake] (version 2.8.12.2 or later)
  