Update codeeditor.h

Author: chrchr-github

gui/codeeditor.h

@@ -65,7 +65,7 @@ class Highlighter : public QSyntaxHighlighter {
         RuleRole ruleRole;
     };
 
-    void applyFormat(HighlightingRule &rule);
+    void applyFormat(HighlightingRule &rule) const;
 
     QList<HighlightingRule> mHighlightingRules;
     QList<HighlightingRule> mHighlightingRulesWithSymbols;