[shotwell] Suppress error on git version check

[Jens Georg <jensgeorg src gnome org>]

commit 708d0aca71a2369a6b56ba2292c9c77792b196fd
Author: Jens Georg <mail jensge org>
Date:   Tue Nov 29 23:57:43 2016 +0100

    Suppress error on git version check
    
    Signed-off-by: Jens Georg <mail jensge org>

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index a62e957..2f94986 100644
--- a/configure.ac
+++ b/configure.ac
@@ -13,7 +13,7 @@ m4_define([api_version],[major_version])
 
 AX_IS_RELEASE([micro-version])
 
-m4_define([git_version],[m4_esyscmd(git rev-parse HEAD)])
+m4_define([git_version],[m4_esyscmd(git rev-parse HEAD 2>/dev/null)])
 
 dnl ***********************************************************************
 dnl Initialize autoconf