Update README.md / Fix a bug in README demo code

[erichuang0771]

Looks like this is a bug in README file, the template is trying to reference something that can be destroyed in memory.

[erichuang0771]

Please fix the same mistake in other places in tutorial readme.md

[szha]

This code base has been donated to the Apache MXNet project per #373, and repo is deprecated. Future development should continue in Apache MXNet.

[CLAassistant]

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