tar: include missing limits.h

Without this header the build fails when used as a OpenWrt build
dependency.

Signed-off-by: Paul Spooren <mail@aparcar.org>

src/tar.c

@@ -9,6 +9,7 @@
 
 #include <sys/stat.h>
 #include <sys/sysmacros.h>
+#include <limits.h>
 
 #include "apk_defines.h"
 #include "apk_tar.h"