Update sidebar processing to reflect Atlas changes

Atlas recently decided to go more "semantic" so sidebar headings are now
H1s. This should therefore be reflected in our script.

Author: delfanbaum

jupyter_book_to_htmlbook/text_processing.py

@@ -72,6 +72,6 @@ def process_sidebars(chapter):
 
         if aside.find("p", class_="sidebar-title"):
             title = aside.find("p", class_="sidebar-title")
-            title.name = "h5"
+            title.name = "h1"
 
     return chapter

tests/test_text_processing.py

@@ -96,4 +96,4 @@ def test_sidebar_processing():
 </aside>""", "html.parser")
     process_sidebars(chapter_text)
     assert chapter_text.find("aside")["data-type"] == "sidebar"
-    assert chapter_text.find("h5").string == "Here Is a Sidebar Title"
+    assert chapter_text.find("h1").string == "Here Is a Sidebar Title"