Replaced spaces on tabs (#3555)

.gitmodules

@@ -5,8 +5,8 @@
 	path = cmake/external/googletest
 	url = https://github.com/google/googletest.git
 [submodule "cmake/external/onnx"]
-  path = cmake/external/onnx
-  url = https://github.com/onnx/onnx
+	path = cmake/external/onnx
+	url = https://github.com/onnx/onnx
 [submodule "cmake/external/tvm"]
 	path = cmake/external/tvm
 	url = https://github.com/microsoft/onnxruntime-tvm.git