Integrated the new span class

src/renderer/renderer.rs

@@ -85,7 +85,10 @@ impl<'a> DustRenderer<'a> {
         let mut output = String::new();
         for elem in &body.elements {
             match elem {
-                TemplateElement::TESpan(span) => output.push_str(span.contents),
+                TemplateElement::TESpan(span) => span
+                    .contents
+                    .iter()
+                    .for_each(|line: &&str| output.push_str(line)),
                 TemplateElement::TETag(dt) => {
                     output.push_str(&self.render_tag(dt, context)?);
                 }