Fix issue with surrogate pairs messing up links at EOL

The closing code for entity items was sometimes not run at the end of a block if the block text included emoji made up of multiple characters.  In cases such as this. string.length !== Array.from(string).length, the latter being a more accurate representation of how many characters there actually are.

Author: Rose Robertson

src/draft-to-markdown.js

@@ -436,7 +436,7 @@ function renderBlock(block, index, rawDraftObject, options) {
 
   // Close any remaining entity tags
   block.entityRanges.forEach(function (range, rangeIndex) {
-    if (range.offset + range.length === block.text.length) {
+    if (range.offset + range.length === Array.from(block.text).length) {
       var entity = rawDraftObject.entityMap[range.key];
       if (customEntityItems[entity.type] || EntityItems[entity.type]) {
         markdownString += (customEntityItems[entity.type] || EntityItems[entity.type]).close(entity);