OS X -> macOS (#1934)

Fix all documentation references of "OS X" to be "macOS", Apple's new brand.

Code is left unchanged because we're matching .NET Core.

docs/learning-powershell/using-vscode.md

@@ -1,7 +1,7 @@
 Using Visual Studio Code for PowerShell Development
 ====
 
-If you are working on Linux and OS X, you cannot use the PowerShell ISE because it is not supported on these platforms.
+If you are working on Linux and macOS, you cannot use the PowerShell ISE because it is not supported on these platforms.
 In this case, you can choose your favorite editor to write PowerShell scripts.
 Here we choose Visual Studio Code as a PowerShell editor.
 
@@ -16,7 +16,7 @@ Editing with Visual Studio Code
 
 * **Linux**: follow the installation instructions on the [Running VS Code on Linux](https://code.visualstudio.com/docs/setup/linux) page
 
-* **OS X**: follow the installation instructions on the [Running VS Code on OS X](https://code.visualstudio.com/docs/setup/osx) page
+* **macOS**: follow the installation instructions on the [Running VS Code on macOS](https://code.visualstudio.com/docs/setup/osx) page
 
   **NOTE:** On OS X you must install OpenSSL for the PowerShell extension to work correctly.  The easiest way to
             accomplish this is to install [Homebrew](http://brew.sh/) and then run `brew install openssl`.  The PowerShell extension
@@ -30,7 +30,7 @@ Editing with Visual Studio Code
 -	Launch the Visual Studio Code app by:    
   *	**Windows**:      typing **code** in your PowerShell session
   *	**Linux**:        typing **code .** in your terminal
-  *	**OS X**:         typing **code** in your terminal
+  *	**macOS**:         typing **code** in your terminal
 
 
 -	Press **F1** (or **Ctrl+Shift+P**) which opens up the "Command Palette" inside the Visual Studio Code app.
@@ -64,7 +64,7 @@ you will need to add a new variable to your user settings file.
     // On Linux:
     "powershell.developer.powerShellExePath": "/opt/microsoft/powershell/<version>/powershell"
 
-    // On OS X:
+    // On macOS:
     "powershell.developer.powerShellExePath": "/usr/local/microsoft/powershell/<version>/powershell"
   ```