Fix PEP8 spacing issues and lint the code

Author: ArtyomVancyan

src/django_mermaid/templatetags/mermaid.py

@@ -55,7 +55,7 @@ def startmermaid(parser, token):
     else:
         theme = None
 
-    nodelist = parser.parse(('endmermaid',))
+    nodelist = parser.parse(("endmermaid",))
     parser.delete_first_token()
 
     return MermaidNode(nodelist, theme)

tests/test_package.py

@@ -13,20 +13,21 @@
 
     site_packages = sysconfig.get_paths()["purelib"]
 
+
 @override_settings(MERMAID_USE_CDN=False)
-@patch('django_mermaid.apps.download_if_necessary')
+@patch("django_mermaid.apps.download_if_necessary")
 def test_download_called_when_use_cdn_false(mock_download):
     # Re-run the AppConfig.ready() method manually
-    app_config = apps.get_app_config('django_mermaid')
+    app_config = apps.get_app_config("django_mermaid")
     app_config.ready()
 
     mock_download.assert_called_once()
 
 
 @override_settings(MERMAID_USE_CDN=True)
-@patch('django_mermaid.apps.download_if_necessary')
+@patch("django_mermaid.apps.download_if_necessary")
 def test_download_not_called_when_use_cdn_true(mock_download):
-    app_config = apps.get_app_config('django_mermaid')
+    app_config = apps.get_app_config("django_mermaid")
     app_config.ready()
 
     mock_download.assert_not_called()

tests/test_tag.py

@@ -120,5 +120,3 @@ def test_tag_use_custom_theme_variables_with_base_theme(version, template_code):
             "<script>mermaid.initialize({\"startOnLoad\": true, \"theme\": \"base\", \"themeVariables\": "
             "{\"primaryColor\": \"#efefef\"}});</script>" % version
     )
-
-