Rename "Mac OS X" to "macOS" in comments

This only changes references in text for human consumption. It leaves
out renaming paths because that can cause breaking changes.

Related issue sorin-ionescu#1449.

modules/command-not-found/init.zsh

@@ -13,8 +13,8 @@ if [[ -s '/etc/zsh_command_not_found' ]]; then
 elif [[ -s '/usr/share/doc/pkgfile/command-not-found.zsh' ]]; then
   source '/usr/share/doc/pkgfile/command-not-found.zsh'
 # Load command-not-found on macOS when homebrew tap is configured.
-elif [[ -s '/usr/local/Homebrew/Library/Taps/homebrew/homebrew-command-not-found/handler.sh' ]]; then
-  source '/usr/local/Homebrew/Library/Taps/homebrew/homebrew-command-not-found/handler.sh'
+elif (( $+commands[brew] )) && brew command command-not-found-init > /dev/null 2>&1; then
+  eval "$(brew command-not-found-init)"
 # Return if requirements are not found.
 else
   return 1