Fix id keyword check in core.py [fixes #28]

Changed the id keyword check to a string for correct dictionary key referencing. This ensures that the element ID assignment works as expected when passed in kwargs.

puepy/core.py

@@ -120,7 +120,7 @@ def __init__(
         else:
             raise Exception("No page passed")
 
-        if id in kwargs:
+        if "id" in kwargs:
             self._element_id = kwargs["id"]
         elif self._page and self._page.application:
             self._element_id = self._page.application.element_id_generator.get_id_for_element(self)