Fix runtime error on Mac OS

[lcd1232]

Closes #13

[ghost]

Sider has detected 2 warnings on analyzing the commit 1b80b93.

• ⚠️ Goodcheck
• ⚠️ Querly

If the errors persist even after retrying, the following actions may resolve them:

• Update tool dependencies
• Configure failed tools
• Configure sider.yml
• Turn off unused tools

If you still have problems, feel free to ask us via chat. 💬

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[Yegorov]

Perhaps you need to check it in not for Windows OS.
For example:

if Yadisk::OS.mac_os? # need implement this method
  output = IO.popen("wget").read
  abort! unless $?.to_i == 0
  return
end