dev-cmd/bottle: require arg for --root-url

Library/Homebrew/dev-cmd/bottle.rb

@@ -106,7 +106,7 @@ module Homebrew
         depends_on: "--write",
         description: "When passed with `--write`, a new commit will not generated after writing changes "\
                      "to the formula file."
-      flag   "--root-url",
+      flag   "--root-url=",
         description: "Use the specified <URL> as the root of the bottle's URL instead of Homebrew's default."
       switch :verbose
       switch :debug

Library/Homebrew/test/dev-cmd/bottle_spec.rb

@@ -12,6 +12,11 @@ describe "brew bottle", :integration_test do
         .and not_to_output.to_stdout
         .and be_a_failure
 
+      expect { brew "bottle", "--root-url" }
+        .to output(/missing argument: --root-url/).to_stderr
+        .and not_to_output.to_stdout
+        .and be_a_failure
+
       setup_test_formula "testball"
 
       # `brew bottle` should not fail with dead symlink