Introduce pyupgrade

Closes #1742 (closed)

Introducing pyupgrade.

Again, I've made one commit per rule.

arkindex/documents/tests/commands/test_load_export.py

@@ -54,7 +54,7 @@ class TestLoadExport(FixtureTestCase):
             "documents.classification": ["ml_class"],
         }
 
-        with open(path, "r") as file:
+        with open(path) as file:
             data = json.loads(file.read())
 
         results = []