Fixed typo in EditorFactory serializePlainText

An empty text file should be serialized as `''` so fix
checking if the document only contains an empty code block
which type is `codeBlock` on tiptap v2 not `code_block`.

Signed-off-by: Ferdinand Thiessen <[email protected]>

Author: susnux

src/EditorFactory.js

@@ -140,7 +140,7 @@ const serializePlainText = (tiptap) => {
 	const doc = tiptap.getJSON()
 
 	if (doc.content.length !== 1 || typeof doc.content[0].content === 'undefined' || doc.content[0].content.length !== 1) {
-		if (doc.content[0].type === 'code_block' && typeof doc.content[0].content === 'undefined') {
+		if (doc.content[0].type === 'codeBlock' && typeof doc.content[0].content === 'undefined') {
 			return ''
 		}
 		throw new SerializeException('Failed to serialize document to plain text')