Stringify dev-cmd/audit `text` variables when used in Regexp matching

- To have the audit commands continue to work, and the tests passing
  (the previous error was [1]), everywhere we're trying to
  `.match?(text)`, instead do `.match?(text.to_s)`.

[1] 5) Homebrew::FormulaAuditor#audit_file __END__ but no DATA
    Failure/Error: fa.audit_file

    TypeError:
      no implicit conversion of Homebrew::FormulaText into String
    # ./dev-cmd/audit.rb:267:in `match?'
    # ./dev-cmd/audit.rb:267:in `audit_file'
    # ./test/dev-cmd/audit_spec.rb:137:in `block (3 levels) in <module:Homebrew>'