Environment details

• OS: Mac OS Catalina v10.15.3
• Ruby version: ruby 2.6.5p114
• Gem name and version: google-cloud-storage

Steps to reproduce

1. Pass "response-content-disposition" => "attachment; filename=\"test 1.txt\"" as a query parameter with a file name that has space in between.
2. You will get a SignatureDoesNotMatchThe request signature we calculated does not match the signature you provided error.

Code example

storage = Google::Cloud::Storage.new(project_id: 'xxx-project-id, credentials: 'credentials_path/config.json')
bucket = storage.bucket('my-bucket-name)
bucket.signed_url('filepath/filename.txt', version: :v4, expires: 3600, headers: nil, query: {"response-content-disposition"=>"attachment; filename=\"test 1.txt\""}, method: :GET)

Full backtrace

No back trace because it still provides you a signed url. It's just that when you use the url you will seem something like:

SignatureDoesNotMatchThe request signature we calculated does not match the signature you provided. Check your Google secret key and signing method.

The issue is that CGI.escape converts the spaces into '+' which is not the %XX UTF-8 style that you guys expected.
Your test cases pass because you guys used URI to parse the url. URI uses %20 for spaces.

I did a quick fork on the master branch to try out fixing it and it works. Do have a look and let me know if I should do a PR for it. cfactolerin@90cf55c

Thanks!