chore: Upgrade Python syntax with pyupgrade

Run with the following pre-commit configuration:

```
repos:
  - repo: https://github.com/asottile/pyupgrade
    rev: v3.1.0
    hooks:
      - id: pyupgrade
        args: [ "--py3-plus", "--py36-plus", "--py37-plus" ]
```

The rationale for every change can be found at https://github.com/asottile/pyupgrade

django_migration_linter/cache.py

@@ -6,20 +6,20 @@ class Cache(dict):
     def __init__(self, django_folder, database, cache_path):
         self.filename = os.path.join(
             cache_path,
-            "{0}_{1}.pickle".format(django_folder.replace(os.sep, "_"), database),
+            "{}_{}.pickle".format(django_folder.replace(os.sep, "_"), database),
         )
 
         if not os.path.exists(os.path.dirname(self.filename)):
             os.makedirs(os.path.dirname(self.filename))
 
-        super(Cache, self).__init__()
+        super().__init__()
 
     def load(self):
         try:
             with open(self.filename, "rb") as f:
                 tmp_dict = pickle.load(f)
                 self.update(tmp_dict)
-        except IOError:
+        except OSError:
             pass
 
     def save(self):