better log for "Check max_depth and num_leaves" (#931)

* better log for "Check max_depth and num_leaves"

The default log said "[LightGBM] [Warning] Accuarcy may be bad since you didn't set num_leaves." but the case max_depth²>num_leaves could also trigger this log.
Correction of a typo too : Accuarcy > Accuracy

* Update config.cpp

src/io/config.cpp

@@ -230,7 +230,7 @@ void OverallConfig::CheckParamConflict() {
     int full_num_leaves = static_cast<int>(std::pow(2, boosting_config.tree_config.max_depth));
     if (full_num_leaves > boosting_config.tree_config.num_leaves 
         && boosting_config.tree_config.num_leaves == kDefaultNumLeaves) {
-      Log::Warning("Accuarcy may be bad since you didn't set num_leaves.");
+      Log::Warning("Accuracy may be bad since you didn't set num_leaves and max_depth² > num_leaves.");
     }
   }
 }