doc: update to use macOS throughout docs

fixes #1499

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

Author: dbkinder

doc/getting_started/getting_started.rst

@@ -12,7 +12,7 @@ Set Up the Development Environment
 The Zephyr project supports these operating systems:
 
 * Linux
-* Mac OS
+* macOS
 * Windows 8.1
 
 Use the following procedures to create a new development environment.
@@ -49,7 +49,7 @@ section will describe the pieces necessary for creating a Zephyr application.
 The processes to build and run a Zephyr application are the same across
 operating systems. Nevertheless, the commands needed do differ from one OS to
 the next. The following sections contain the commands used in a Linux
-development environment. If you are using Mac OS please use the appropriate
+development environment. If you are using macOS please use the appropriate
 commands for your OS.
 
 Building a Sample Application

doc/getting_started/installation_mac.rst

@@ -1,12 +1,12 @@
 .. _installing_zephyr_mac:
 
-Development Environment Setup on Mac OS
-#######################################
+Development Environment Setup on macOS
+######################################
 
-This section describes how to set up a Mac OS development system.
+This section describes how to set up a macOS development system.
 
 After completing these steps, you will be able to compile and run your Zephyr
-applications on the following Mac OS version:
+applications on the following macOS version:
 
 * Mac OS X 10.11 (El Capitan)
 * macOS Sierra 10.12

doc/release-notes-1.5.rst

@@ -102,7 +102,7 @@ Documentation
 - Moved all the boards documentation to the wiki.
 - Moved Code Contribution documentation to the wiki.
 - Added package "ncurses" to the list of requirements.
-- Updated Mac OS X instructions.
+- Updated macOS instructions.
 
 Test and Samples
 ****************