The error message is as follows:
Cloning into 'gramine'...
fatal: unable to access 'https://github.com/gramineproject/gramine.git/': GnuTLS recv error (-110): The TLS connection was non-properly terminated.
I. Temporary solutions
git clone --recursive 'https://github.com/valloric/youcompleteme.git
Second, the permanent solution
Solution (execute the following codes sequentially):
apt-get install gnutls-bin
git config --global http.sslVerify false
git config --global http.postBuffer 1048576000