Change the format used for sprintbuf (but not scanf) to use %f instead of %lf because the "l" is unnecessary and some compilers behave differently with it present (e.g. MinGW).

Thanks for Mateusz Loskot for the fix.

json_object.c

@@ -463,7 +463,7 @@ static int json_object_double_to_json_string(struct json_object* jso,
 					     int level,
 						 int flags)
 {
-  return sprintbuf(pb, "%lf", jso->o.c_double);
+  return sprintbuf(pb, "%f", jso->o.c_double);
 }
 
 struct json_object* json_object_new_double(double d)