[ADD] converter of clear_display function and fix a bug

Author: rikutons

src/lib/ruby-to-blocks-converter/microbit.js

@@ -61,13 +61,20 @@ const MicroBitConverter = {
                 break;
             case 'display_text':
                 if (args.length === 1 && this._isString(args[0])) {
-                    block = this._changeBlock(receiver, 'microbit_displayText', 'sentence');
+                    block = this._changeBlock(receiver, 'microbit_displayText', 'statement');
                     delete this._context.blocks[receiver.inputs.EXPRESSION.block];
                     delete receiver.inputs.EXPRESSION;
 
                     this._addTextInput(block, 'TEXT', args[0], 'Hello!');
                 }
                 break;
+            case 'clear_display':
+                if (args.length === 0) {
+                    block = this._changeBlock(receiver, 'microbit_displayClear', 'statement');
+                    delete this._context.blocks[receiver.inputs.EXPRESSION.block];
+                    delete receiver.inputs.EXPRESSION;
+                }
+                break;
             }
         }
         return block;