Build overview: link to commit comparison (#12292)

The text says we are comparing against a commit, so why not link to the
commit comparison page.

GH will render this as
4617dfa...ea12f92

Author: stsewd

readthedocs/builds/tests/test_tasks.py

@@ -208,7 +208,7 @@ def test_post_build_overview(self, get_diff, post_comment):
 
             ### Files changed
 
-            > Comparing with [latest](http://my-project.readthedocs.io/en/latest/) (1234abcd)
+            > Comparing with [latest](http://my-project.readthedocs.io/en/latest/) (1234abcd...5678abcd)
 
 
             <details>
@@ -257,7 +257,7 @@ def test_post_build_overview_more_than_5_files(self, get_diff, post_comment):
 
             ### Files changed
 
-            > Comparing with [latest](http://my-project.readthedocs.io/en/latest/) (1234abcd)
+            > Comparing with [latest](http://my-project.readthedocs.io/en/latest/) (1234abcd...5678abcd)
 
 
             <details>
@@ -302,7 +302,7 @@ def test_post_build_overview_no_files_changed(self, get_diff, post_comment):
 
             ### Files changed
 
-            > Comparing with [latest](http://my-project.readthedocs.io/en/latest/) (1234abcd)
+            > Comparing with [latest](http://my-project.readthedocs.io/en/latest/) (1234abcd...5678abcd)
 
 
             No files changed.

readthedocs/templates/core/build-overview.md

@@ -10,7 +10,7 @@ make sure to adjust the tags accordingly, as they introduce newlines.
 
 ### Files changed
 
-> Comparing with [{{ base_version.verbose_name }}]({{ base_version.get_absolute_url }}) ({{ base_version_build.commit }})
+> Comparing with [{{ base_version.verbose_name }}]({{ base_version.get_absolute_url }}) ({{ base_version_build.commit }}...{{ current_version_build.commit }})
 
 {% if diff.files %}
 <details>