Fix markdown formatting

CHANGELOG.txt

@@ -4,7 +4,7 @@ Changelog
 1.7 (xx.xx.xxxx)
 ~~~~~~~~~~~~~~~~
 
- * The Wagtail version number can now be obtained as a tuple using ``from wagtail import VERSION`` (Tim Heap)
+ * The Wagtail version number can now be obtained as a tuple using `from wagtail import VERSION` (Tim Heap)
  * Fix: Migrations for wagtailcore and project template are now reversible (Benjamin Bach)
  * Fix: The default image format label text ('Full width', 'Left-aligned', 'Right-aligned') is now localised (Mikalai Radchuk)