Possessive "it" (#7357)

"it's" → "its"

CONTRIBUTORS.rst

@@ -524,6 +524,7 @@ Contributors
 * Daniel Fairhead
 * Kevin Gutiérrez
 * Brandon Murch
+* Sean Kelly
 
 Translators
 ===========

docs/getting_started/tutorial.md

@@ -191,7 +191,7 @@ Edit `home/templates/home/home_page.html` to contain the following:
 ### Wagtail template tags
 
 In addition to Django's [template tags and filters](https://docs.djangoproject.com/en/3.1/ref/templates/builtins/),
-Wagtail provides a number of it's own [template tags & filters](template-tags-and-filters)
+Wagtail provides a number of its own [template tags & filters](template-tags-and-filters)
 which can be loaded by including `{% load wagtailcore_tags %}` at the top of
 your template file.
 
@@ -864,4 +864,4 @@ Finally, we can update the `blog_page.html` template to display the categories:
 
 -   Read the Wagtail [topics](../topics/index) and [reference](../reference/index) documentation
 -   Learn how to implement [StreamField](../topics/streamfield) for freeform page content
--   Browse through the [advanced topics](../advanced_topics/index) section and read [third-party tutorials](../advanced_topics/third_party_tutorials)
+-   Browse through the [advanced topics](../advanced_topics/index) section and read [third-party tutorials](../advanced_topics/third_party_tutorials)