FormulaInstaller#sanitized_ARGV_options: fix regex

This fixes a regression caused by 2e961dc9dee63f641f7f162fd7a2845c5fd092fe,
where a misplaced `+` cause the regex only catch one character.

Fixes https://github.com/Homebrew/homebrew-science/issues/3847.

Library/Homebrew/formula_installer.rb

@@ -535,7 +535,7 @@ class FormulaInstaller
     end
 
     formula.options.each do |opt|
-      name = opt.name[/^([^=])+=$/, 1]
+      name = opt.name[/^([^=]+)=$/, 1]
       value = ARGV.value(name) if name
       args << "--#{name}=#{value}" if value
     end