git: update to v2.8.2

Update to git version v2.8.2.

* Upstream commit 1a0c8dfd89475d6bb09ddee8c019cf0ae5b3bdc2 (strbuf: give
  strbuf_getline() to the "most text friendly" variant) changed API.

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

Makefile

@@ -14,7 +14,7 @@ htmldir = $(docdir)
 pdfdir = $(docdir)
 mandir = $(prefix)/share/man
 SHA1_HEADER = <openssl/sha.h>
-GIT_VER = 2.7.2
+GIT_VER = 2.8.2
 GIT_URL = https://www.kernel.org/pub/software/scm/git/git-$(GIT_VER).tar.gz
 INSTALL = install
 COPYTREE = cp -r