Update to SPDX 3.1

[legoktm]

https://lists.spdx.org/pipermail/spdx-legal/2018-April/002554.html

No major changes, a few renames, new licenses and deprecation of AGPL-1.0 in favor of -only/-or-later versions.

[codecov-io]

Codecov Report

Merging #20 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #20   +/-   ##
=========================================
  Coverage     97.56%   97.56%           
  Complexity       43       43           
=========================================
  Files             2        2           
  Lines           123      123           
=========================================
  Hits            120      120           
  Misses            3        3

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[alcohol]

LGTM