[Doc] EdgeWeightNorm Fix doc (#3051)

Co-authored-by: Jinjing Zhou <VoVAllen@users.noreply.github.com>

python/dgl/nn/pytorch/conv/graphconv.py

@@ -21,12 +21,12 @@ class EdgeWeightNorm(nn.Module):
 
     Mathematically, setting ``norm='both'`` yields the following normalization term:
 
-    .. math:
+    .. math::
       c_{ji} = (\sqrt{\sum_{k\in\mathcal{N}(j)}e_{jk}}\sqrt{\sum_{k\in\mathcal{N}(i)}e_{ki}})
 
     And, setting ``norm='right'`` yields the following normalization term:
 
-    .. math:
+    .. math::
       c_{ji} = (\sum_{k\in\mathcal{N}(i)}}e_{ki})
 
     where :math:`e_{ji}` is the scalar weight on the edge from node :math:`j` to node :math:`i`.