Update Extract.h

Extract.h

@@ -43,7 +43,7 @@ static bool optimize_string (std::string &str, std::string &last);
 // EFFECTS: returns false if a new text is detected by the '-' symbol
 // returns false if the text is a continuation of
 // previous text with a newline 
-static bool is_continued_text (const std::string str);
+static bool is_continued_text (const std::string &str);
 
 class Extract {
 public: