TextEditor: Let's have line numbers starting at 1.

Thanks to Dan for pointing this out on IRC:

<danboid> I see TextEditor still numbers its lines from 0. You're too much of a programmer sometimes kling! :)
<  kling> that might be the most extreme form of "programmer design" I've seen in serenity

Libraries/LibGUI/GTextEditor.cpp

@@ -292,7 +292,7 @@ void GTextEditor::paint_event(GPaintEvent& event)
             auto ruler_line_rect = ruler_content_rect(i);
             painter.draw_text(
                 ruler_line_rect.shrunken(2, 0),
-                String::number(i),
+                String::number(i + 1),
                 is_current_line ? Font::default_bold_font() : font(),
                 TextAlignment::CenterRight,
                 is_current_line ? Color::DarkGray : Color::MidGray);