fix cmake format

python/CMakeLists.txt

@@ -15,7 +15,7 @@ set(PY_FILES paddle/__init__.py
 configure_file(${CMAKE_CURRENT_SOURCE_DIR}/setup.py.in
     ${CMAKE_CURRENT_BINARY_DIR}/setup.py)
 
-  add_custom_command(OUTPUT ${OUTPUT_DIR}/.timestamp
+add_custom_command(OUTPUT ${OUTPUT_DIR}/.timestamp
     COMMAND env ${py_env} ${PYTHON_EXECUTABLE} setup.py bdist_wheel
     COMMAND ${CMAKE_COMMAND} -E touch ${OUTPUT_DIR}/.timestamp
     DEPENDS gen_proto_py ${PY_FILES} ${external_project_dependencies} paddle_master_shared)