Fixed typo and error msg

hpvm/projects/onnx/frontend/graph_ir.py

@@ -5,21 +5,21 @@
 
 class DFGNode(object):
     def __init__(self, onnx_node):
-        #self.onnx_node = onnx_node
+        # self.onnx_node = onnx_node
         self.name = onnx_node.name
         self.op_type = onnx_node.op_type
         self.input = onnx_node.input
         self.output = onnx_node.output
 
     def codegen(self, tensors):
-        return "Not Implemented."
+        return "\n***Not Implemented***\n"
 
     def hpvm_codegen(self, tensors):
-        return "Not Implemented."
+        return "\n***Not Implemented***\n"
 
 
 '''
-Element wise operatos that is for activation function
+Element wise operators that is for activation function
 e.g. HardSigmoid, LeakyRelu, PRelu, Pow, Reciprocal,
 Relu, Selu, Sigmoid, Softplus, Sqrt, ThresholdedRelu,
 Abs, Ceil, Elu, Floor, Neg