安装自定义brew公式时未定义的方法“cmd”

我正在创建一个 Homebrew 公式:

class Pouet < Formula
  desc "A basic command line application written with Qt"
  homepage "https://github.com/MartinDelille/pouet"
  url "https://github.com/MartinDelille/pouet"
  version "0.1"
  sha256 "d4222bde4c798bc4d7f0a5566079d9095d4e4996bc53fe8fc76e63325aa0e71c"
  depends_on "qt" # => :build

  def install
    system "qmake", "pouet.pro"
    system "make"
    bin.install "pouet"
  end

  test do
    system "#{bin}/pouet"
  end
end

$ brew install pouet
==> Installing pouet from martindelille/tap
==> Downloading https://github.com/MartinDelille/pouet
Already downloaded: /Users/martin/Library/Caches/Homebrew/downloads/e2994828582a29cbbcc10eac093db7f4c95aab2139f30033de5ed3ed3a3f4ab9--pouet
/usr/local/Homebrew/Library/Homebrew/build.rb:206:in `rescue in <main>': undefined method `cmd' for #<ChecksumMismatchError:0x00007fcad2a0cae0> (NoMethodError)
    from /usr/local/Homebrew/Library/Homebrew/build.rb:183:in `<main>'
Error: Failure while executing; `/usr/bin/sandbox-exec -f /private/tmp/homebrew20181226-5110-o03zk0.sb nice /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby -W0 -I /usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/ruby-macho-2.1.0/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/rubocop-rspec-1.30.1/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/rubocop-0.61.1/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/unicode-display_width-1.4.0/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/ruby-progressbar-1.10.0/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/rainbow-3.0.0/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/powerpack-0.1.2/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/plist-3.4.0/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/parser-2.5.3.0/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/parallel-1.12.1/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/jaro_winkler-1.5.1/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/extensions/universal-darwin-18/2.3.0/jaro_winkler-1.5.1:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/backports-3.11.4/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/ast-2.4.0/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/activesupport-5.2.2/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/tzinfo-1.2.5/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/thread_safe-0.3.6/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/minitest-5.11.3/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/i18n-1.3.0/lib:/usr/local/Homebrew/Library/Homebrew/vendor/bundle-standalone/bundler/../ruby/2.3.0/gems/concurrent-ruby-1.1.4/lib:/Library/Ruby/Gems/2.3.0/gems/did_you_mean-1.0.0/lib:/Library/Ruby/Site/2.3.0:/Library/Ruby/Site/2.3.0/x86_64-darwin17:/Library/Ruby/Site/2.3.0/universal-darwin17:/Library/Ruby/Site:/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/vendor_ruby/2.3.0:/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/vendor_ruby/2.3.0/x86_64-darwin17:/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/vendor_ruby/2.3.0/universal-darwin17:/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/vendor_ruby:/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0:/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/x86_64-darwin17:/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/universal-darwin17:/usr/local/Homebrew/Library/Homebrew -- /usr/local/Homebrew/Library/Homebrew/build.rb /usr/local/Homebrew/Library/Taps/martindelille/homebrew-tap/pouet.rb` exited with 1.