README: s/git/https/ (#2493)

git clone git://github.com is not expected to work since quite some time and just hangs

Author: ygrek

README.md

@@ -46,7 +46,7 @@ domain-specific language for analysis problems.
 
 Use git to obtain the source code of Soufflé.
 
-    $ git clone git://github.com/souffle-lang/souffle.git
+    $ git clone https://github.com/souffle-lang/souffle.git
 
 Build instructions can be found [here](https://souffle-lang.github.io/build).