--cellar: use CLI::Parser.

Library/Homebrew/cmd/--cellar.rb

-#:  * `--cellar`:
-#:    Display Homebrew's Cellar path. *Default:* `$(brew --prefix)/Cellar`, or if
-#:    that directory doesn't exist, `$(brew --repository)/Cellar`.
-#:
-#:  * `--cellar` <formula>:
-#:    Display the location in the cellar where <formula> would be installed,
-#:    without any sort of versioned directory as the last path.
+require "cli_parser"
 
 module Homebrew
   module_function
 
+  def __cellar_args
+    Homebrew::CLI::Parser.new do
+      usage_banner <<~EOS
+        `--cache` [<formula>]
+
+        Display Homebrew's Cellar path. *Default:* `$(brew --prefix)/Cellar`, or if
+        that directory doesn't exist, `$(brew --repository)/Cellar`.
+
+        If <formula> is provided, display the location in the cellar where <formula>
+        would be installed, without any sort of versioned directory as the last path.
+      EOS
+    end
+  end
+
   def __cellar
+    __cellar_args.parse
+
     if ARGV.named.empty?
       puts HOMEBREW_CELLAR
     else