Fix alt header test

src/lib.rs

@@ -265,9 +265,12 @@ Paragraph 4",
         let doc = parse(
             "\
 Text
-Header
-------
-More text",
+Header 1
+========
+More text
+Header 2
+--------
+",
         );
         let doc_ref = Document(vec![
             Node::Paragraph(vec![StyledText {
@@ -278,7 +281,7 @@ More text",
                 text: "Text".to_string(),
             }]),
             Node::Header(Header {
-                label: "Header".to_string(),
+                label: "Header 1".to_string(),
                 level: 1,
             }),
             Node::Paragraph(vec![StyledText {
@@ -288,6 +291,10 @@ More text",
                 color: None,
                 text: "More text".to_string(),
             }]),
+            Node::Header(Header {
+                label: "Header 2".to_string(),
+                level: 2,
+            }),
         ]);
 
         assert_eq!(doc, doc_ref);