Include stdint.h in git2/config.h

Otherwise MSVC doesn't know what we're talking about when we say
int32_t or int64_t.

Signed-off-by: Carlos Martín Nieto <carlos@cmartin.tk>

include/git2/config.h

@@ -9,6 +9,7 @@
 
 #include "common.h"
 #include "types.h"
+#include <stdint.h>
 
 /**
  * @file git2/config.h