git: update for v2.3.0

* sort_string_list(): rename to string_list_sort() (upstream commit
  3383e199)
* update read_tree_recursive callback to pass strbuf as base (upstream
  commit 6a0b0b6d)

Signed-off-by: Christian Hesse <mail@eworm.de>

Makefile

@@ -14,7 +14,7 @@ htmldir = $(docdir)
 pdfdir = $(docdir)
 mandir = $(prefix)/share/man
 SHA1_HEADER = <openssl/sha.h>
-GIT_VER = 2.2.2
+GIT_VER = 2.3.0
 GIT_URL = https://www.kernel.org/pub/software/scm/git/git-$(GIT_VER).tar.gz
 INSTALL = install
 COPYTREE = cp -r