add a prototype declaration for mrb_fiber_resume(); ref #1269

include/mruby.h

@@ -425,6 +425,7 @@ MRB_API mrb_bool mrb_respond_to(mrb_state *mrb, mrb_value obj, mrb_sym mid);
 MRB_API mrb_bool mrb_obj_is_instance_of(mrb_state *mrb, mrb_value obj, struct RClass* c);
 
 /* fiber functions (you need to link mruby-fiber mrbgem to use) */
+MRB_API mrb_value mrb_fiber_resume(mrb_state *mrb, mrb_value fib, mrb_int argc, const mrb_value *argv);
 MRB_API mrb_value mrb_fiber_yield(mrb_state *mrb, mrb_int argc, const mrb_value *argv);
 #define E_FIBER_ERROR (mrb_class_get(mrb, "FiberError"))