Fix readme: libgit2 version

Author: Stephan Dilly

README.md

@@ -16,7 +16,7 @@ stable release as well.
 
 ## Version of libgit2
 
-Currently this library requires libgit2 1.1.0. The source for libgit2 is
+Currently this library requires libgit2 1.3.0. The source for libgit2 is
 included in the libgit2-sys crate so there's no need to pre-install the libgit2
 library, the libgit2-sys crate will figure that and/or build that for you.