title: packagist error when adding bitbucket repository
body: <p>I get the following error when trying to add a repository.</p>
  
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  <p>Uncaught Exception: [RuntimeException] Failed to execute git clone --mirror 'git@bitbucket.org:doppy/doppy.git' '/home/composer/.composer/cache/vcs/git-bitbucket.org-doppy-doppy.git/' Cloning into bare repository '/home/composer/.composer/cache/vcs/git-bitbucket.org-doppy-doppy.git'... Host key verification failed. fatal: Could not read from remote repository. Please make sure you have the correct access rights and the repository exists.</p>
  
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  <p>The repository is public and when I copy and run the command locally I don't get any error.
  I guess this an issue on the packagist server itself with the bitbucket servers?</p>
  
  <p>side note: yeah, I understand it is a silly repo. I fully intend to remove it when done testing and cleanup my own mess.</p>