Update Doc: image prop width change to previewWidth (#1007)

Author: debbbbie

docs/pages/docs/editor-basics/default-schema.mdx

@@ -95,7 +95,7 @@ type ImageBlock = {
   props: {
     url: string = "";
     caption: string = "";
-    width: number = 512;
+    previewWidth: number = 512;
   } & DefaultProps;
   content: undefined;
   children: Block[];
@@ -106,7 +106,7 @@ type ImageBlock = {
 
 `caption:` The image caption.
 
-`width:` The image width in pixels.
+`previewWidth:` The image previewWidth in pixels.
 
 #### Table