Error with https://libgit2.github.com/libgit2.github.com

exception = HTTPSConnectionPool(host='libgit2.github.com', port=443): Max retries exceeded with url: /libgit2.github.com (Caused by NameResolutionError(": Failed to resolve 'libgit2.github.com' ([Errno -5] No address associated with hostname)"))