Switch to SHA256 for the hashing.
Switch to SHA256 for the hashing.

MD5 is known weak nowadays.  We could switch to SHA-1
to be compatible with git itself, but that's also not
that secure anymore, so we jump straight to SHA256.

Signed-off-by: Chris Lalancette <281cd07d7578d97c83271fbbf2faddb83ab3791c@irobot.com>

manuelnaranjo/git-got,jake4679/git-got