Update LICENSE to be public domain.

[AdityaSavara]

The readme says the software is in the public domain. This pull request makes the license file match that. Below are further details.

** The readme says the software is in the public domain. The LICENSE file says it is the MIT license.

Neither of these were added by the navdeep, though the master branch seems to now be the one created by ken-reitz who did add these. Additionally, the readme was recently updated by navdeep:

https://github.com/navdeep-G/setup.py/commit/46f7cd41a5d58adde653aae19c54cf689a3b2a91

From the above, I infer that the correct license should be the Unlicense license. I copied and pasted the text from the github template. Presumably, it is the same as the below link.

https://unlicense.org/

[AdityaSavara]

@navdeep-G It will be useful if you can personally approve the public domain license pull request. That way people can use this setup.py in federal government work without worry.