package/libgit2: bump to version 1.2.0

package/libgit2: bump to version 1.2.0

COPYING was updated with a copy of the openssl licence since libgit2 now
include openssl headers so it can dlopen it:

    openssl: dynamically load libssl and symbols (optionally)

    Provide an interface around OpenSSL to dynamically load the
    libraries and symbols, so that users can distribute a libgit2
    library that is not linked directly against OpenSSL.  This enables
    users to target multiple distributions with a single binary.

    This mechanism is optional and disabled by default.  Configure cmake
    with -DUSE_HTTPS=OpenSSL-Dynamic to use it.

We do not use that option so the headers are not even used, plus the
headers are not installed on the target anyway, so this patch includes
no license changes.

Upstream also stopped providing release tarballs, relying on
github-generated tarballs instead.

Signed-off-by: Nicolas Cavallari <nicolas.cavallari@green-communications.fr>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>