Add missing method to list block.

The list block does not have an on change set for it and is expected to
causing errors and no updating of the block attribute state.  This PR
copies the current implementation from a text block and enters it into
the list block.

blocks/library/list/index.js

@@ -54,18 +54,27 @@ registerBlock( 'core/list', {
 		}
 	],
 
-	edit( { attributes, focus, setFocus } ) {
+	edit( { attributes, setAttributes, focus, setFocus } ) {
 		const { nodeName = 'OL', items = [], align } = attributes;
 		const content = items.map( ( item, i ) => {
 			return <li key={ i }>{ item.value }</li>;
 		} );
 
+		const itemsFromContent = ( listContents ) => {
+			return listContents.map( ( listContent ) => ( { value: listContent.props.children } ) );
+		};
+
 		return (
 			<Editable
 				tagName={ nodeName.toLowerCase() }
 				style={ align ? { textAlign: align } : null }
 				value={ content }
 				focus={ focus }
+				onChange={ ( nextContent ) => {
+					setAttributes( {
+						items: itemsFromContent( nextContent )
+					} );
+				} }
 				onFocus={ setFocus }
 				className="blocks-list" />
 		);