Added comment char for prolog

src/source.cpp

@@ -223,7 +223,7 @@ Source::View::View(const boost::filesystem::path &file_path, const Glib::RefPtr<
   else {
     if(is_language({"cmake", "makefile", "python", "python3", "sh", "perl", "ruby", "r", "asm", "automake", "yaml", "docker", "julia"}))
       comment_characters = "#";
-    else if(is_language({"latex", "matlab", "octave", "bibtex"}))
+    else if(is_language({"latex", "matlab", "octave", "bibtex", "prolog"}))
       comment_characters = "%";
     else if(language_id == "fortran")
       comment_characters = "!";