Fix root LICENSE file.

[BigBlueHat]

Some how the root LICENSE file got reverted to the BSD-3-Clause in all our back-and-forth about other things (across other repos).

This properly uses the Apache-2.0 in that file.

[codecov]

Codecov Report

Merging #118 (fd979de) into main (8e47ff5) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #118   +/-   ##
=======================================
  Coverage   81.45%   81.45%           
=======================================
  Files          10       10           
  Lines        1941     1941           
=======================================
  Hits         1581     1581           
  Misses        360      360           

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