Use literal syntax instead of function calls to create data structure (#47)

Co-authored-by: deepsource-autofix[bot] <62050782+deepsource-autofix[bot]@users.noreply.github.com>

Author: deepsource-autofix[bot]

flask_shell2http/base_entrypoint.py

@@ -65,7 +65,7 @@ def __init_extension(self) -> None:
         For internal use only.
         """
         if not hasattr(self.app, "extensions"):
-            self.app.extensions = dict()
+            self.app.extensions = {}
 
         self.app.extensions["shell2http"] = self