Change documentation references from OS X to macOS (#1927)

Since OS X 10.12 it has been named macOS so it makes sense
to reference it in documentation as such, even when it
sometimes refers to older versions which were called (Mac) OS X.

interface/wx/appprogress.h

@@ -9,7 +9,7 @@
     @class wxAppProgressIndicator
 
     A helper class that can be used to update the progress bar in the taskbar
-    button on Windows and the dock icon on OS X.
+    button on Windows and the dock icon on macOS.
 
     @library{wxcore}
     @category{misc}