[Doc] Fix a typo in edgeconv.py (#5643)

Co-authored-by: Mufei Li <mufeili1996@gmail.com>

python/dgl/nn/tensorflow/conv/edgeconv.py

@@ -56,8 +56,8 @@ class EdgeConv(layers.Layer):
 
     Calling ``add_self_loop`` will not work for some graphs, for example, heterogeneous graph
     since the edge type can not be decided for self_loop edges. Set ``allow_zero_in_degree``
-    to ``True`` for those cases to unblock the code and handle zere-in-degree nodes manually.
-    A common practise to handle this is to filter out the nodes with zere-in-degree when use
+    to ``True`` for those cases to unblock the code and handle zero-in-degree nodes manually.
+    A common practise to handle this is to filter out the nodes with zero-in-degree when use
     after conv.
     """