wrong word in comment: should be signal instead of single.

...confirmed by the similar comment immediately before it.

Change-Id: Id334a81bb9078a761d233631639c007b7bf2c17f
Reviewed-on: https://gerrit.libreoffice.org/40855Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Justin Luth <justin_luth@sil.org>

writerfilter/source/rtftok/rtftokenizer.hxx

@@ -39,7 +39,7 @@ public:
     }
     /// To be invoked by the pushState() callback to signal when the importer enters a group.
     void pushGroup();
-    /// To be invoked by the popState() callback to single when the importer leaves a group.
+    /// To be invoked by the popState() callback to signal when the importer leaves a group.
     void popGroup();
     OUString getPosition();
     std::size_t getGroupStart()