Quote: Restore value map with defined default

Needed to ensure key is assigned into map result to avoid React error. Seems unnecessary since we don't need the diffing reconciliation for generating static markup, but alas.

See: facebook/react#7038

blocks/library/quote/index.js

@@ -29,6 +29,7 @@ registerBlockType( 'core/quote', {
 		value: {
 			type: 'array',
 			source: query( 'blockquote > p', node() ),
+			default: [],
 		},
 		citation: {
 			type: 'array',
@@ -204,7 +205,9 @@ registerBlockType( 'core/quote', {
 				className={ `blocks-quote-style-${ style }` }
 				style={ { textAlign: align ? align : null } }
 			>
-				{ value }
+				{ value.map( ( paragraph, i ) => (
+					<p key={ i }>{ paragraph.props.children }</p>
+				) ) }
 				{ citation && citation.length > 0 && (
 					<footer>{ citation }</footer>
 				) }