Fix heading level for autosave in documentation

autosave was a 4th-level heading, which is inconsistent with all other qualifiers, which are 5th-level.

lib/shoulda/matchers/active_record/association_matcher.rb

@@ -217,7 +217,7 @@ module Shoulda
       #       should belong_to(:organization).touch(true)
       #     end
       #
-      # #### autosave
+      # ##### autosave
       #
       # Use `autosave` to assert that the `:autosave` option was specified.
       #
@@ -468,7 +468,7 @@ module Shoulda
       #       should have_many(:ideas).validate(false)
       #     end
       #
-      # #### autosave
+      # ##### autosave
       #
       # Use `autosave` to assert that the `:autosave` option was specified.
       #
@@ -678,7 +678,7 @@ module Shoulda
       #       should have_one(:parking_card).validate(false)
       #     end
       #
-      # #### autosave
+      # ##### autosave
       #
       # Use `autosave` to assert that the `:autosave` option was specified.
       #
@@ -836,7 +836,7 @@ module Shoulda
       #         validate(false)
       #     end
       #
-      # #### autosave
+      # ##### autosave
       #
       # Use `autosave` to assert that the `:autosave` option was specified.
       #