fix: update close_regex of block menu (#576)

Author: iamsaumya

Diff for: src/plugins/BlockMenuTrigger.tsx

@@ -10,7 +10,7 @@ import Extension from "../lib/Extension";
 
 const MAX_MATCH = 500;
 const OPEN_REGEX = /^\/(\w+)?$/;
-const CLOSE_REGEX = /(^(?!\/(\w+)?)(.*)$|^\/((\w+)\s.*|\s)$)/;
+const CLOSE_REGEX = /(^(?!\/(\w+)?)(.*)$|^\/(([\w\W]+)\s.*|\s)$|^\/((\W)+)$)/;
 
 // based on the input rules code in Prosemirror, here:
 // https://github.com/ProseMirror/prosemirror-inputrules/blob/master/src/inputrules.js