dependencies: fix error in recursive_includes

[Bo98]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew tests with your changes locally?

---

$ brew uses --include-build --include-test --recursive gettext
Error: Failed to import: /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/diesel.rb
undefined local variable or method `formula' for Homebrew:Module
Error: Failed to import: /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/mutt.rb
undefined local variable or method `formula' for Homebrew:Module
Error: Failed to import: /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/haxe.rb
undefined local variable or method `formula' for Homebrew:Module

[MikeMcQuaid]

Thanks @Bo98!