fix submodule url

[mvallebr]

URL is half ssh and half https currently, causing problems on update

[travisjohn-son]

Thanks for this pull request as I just ran into this problem myself. It turned out GitHub no longer supports the old URL format as of last week (March 15, 2022) according to Stack Overflow discussion.

I had to resort to this workaround using the https protocol instead as I used the Installation steps from the README.

git clone https://github.com/datasift/gitflow
cd gitflow
sed -i.bkup 's,git://github.com/,https://github.com/,' .gitmodules
sudo ./install.sh