I had this problem for twitter bootstrap:
[Composer\Downloaded\TransportException] The "https://api.github.com/repos/twitter/bootstrap/zipball/v2.3.1" file could not be written to /my/path/Symfony/vendor/twitter/bootstrap/e01f28f3c03a11c104bae8d4a1b59d21.1:
Performing "composer self-updating" changed it to:
[Composer\Downloader\TransportException] "https://api.github.com/repos/twitter/bootstrap/zipball/v2.3.1" appears broken, and returned an empty 200 response
Using "composer update --prefer-source" seems to have installed it correctly.
So, it looks like the download of the github zip file is broken.
James
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