Merge pull request #1077 from mjoerg/readme-fix-version

README: update reference to libgit2 version

Author: ehuss

README.md

@@ -16,7 +16,7 @@ stable release as well.
 
 ## Version of libgit2
 
-Currently this library requires libgit2 1.7.2 (or newer patch versions). The
+Currently this library requires libgit2 1.8.1 (or newer patch versions). 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. On the other hand, if an appropriate version of `libgit2`