Fixes oppia#1750: When sending emails, convert bullet points in html …

…format to hyphens in text format.

core/domain/email_manager.py

@@ -171,7 +171,7 @@ def _send_email(
         return
 
     raw_plaintext_body = cleaned_html_body.replace('<br/>', '\n').replace(
-        '<br>', '\n').replace('</p><p>', '</p>\n<p>')
+        '<br>', '\n').replace('<li>', '<li>- ').replace('</p><p>', '</p>\n<p>')
     cleaned_plaintext_body = html_cleaner.strip_html_tags(raw_plaintext_body)
 
     if email_models.SentEmailModel.check_duplicate_message(

core/domain/email_manager_test.py

@@ -209,9 +209,9 @@ def test_correct_rights_are_written_in_manager_role_email_body(self):
             ', on Oppia.org.\n'
             '\n'
             'This allows you to:\n'
-            'Change the exploration permissions\n'
-            'Edit the exploration\n'
-            'View and playtest the exploration\n'
+            '- Change the exploration permissions\n'
+            '- Edit the exploration\n'
+            '- View and playtest the exploration\n'
             '\n'
             'You can find the exploration here.\n'
             '\n'
@@ -274,8 +274,8 @@ def test_correct_rights_are_written_in_editor_role_email_body(self):
             ', on Oppia.org.\n'
             '\n'
             'This allows you to:\n'
-            'Edit the exploration\n'
-            'View and playtest the exploration\n'
+            '- Edit the exploration\n'
+            '- View and playtest the exploration\n'
             '\n'
             'You can find the exploration here.\n'
             '\n'
@@ -337,7 +337,7 @@ def test_correct_rights_are_written_in_playtester_role_email_body(self):
             ', on Oppia.org.\n'
             '\n'
             'This allows you to:\n'
-            'View and playtest the exploration\n'
+            '- View and playtest the exploration\n'
             '\n'
             'You can find the exploration here.\n'
             '\n'