fixed typo _detect_loader() -> detect_loader() in celery.loaders.current_loader(). Thanks twillis!

celery/loaders/__init__.py

@@ -81,7 +81,7 @@ def current_loader():
     """Detect and return the current loader."""
     global _loader
     if _loader is None:
-        _loader = _detect_loader()()
+        _loader = detect_loader()()
     return _loader