Fix GitHub license field

[tenderlove]

GitHub doesn't seem to understand what the license is:

I didn't recognize the license file either, but it's actually the 3-Clause BSD license.

I don't think we should change the license, but there must be a way to get GitHub to display the right thing. We probably should update the copyright year and also add "et, al." to the license as well.

[flavorjones]

This is weird, licensee seems to detect it fine:

$ licensee
License:        NOASSERTION
Matched files:  LICENSE, LICENSE-DEPENDENCIES, README.md, sqlite3.gemspec
LICENSE:
  Content hash:  9af635d4936231a9dcddc9fb82fda06054549710
  Attribution:   Copyright (c) 2004, Jamis Buck (jamis@jamisbuck.org)
  Confidence:    98.72%
  Matcher:       Licensee::Matchers::Dice
  License:       BSD-3-Clause
  Closest non-matching licenses:
    BSD-3-Clause similarity:  98.72%
    BSD-4-Clause similarity:  82.44%
    BSD-2-Clause similarity:  81.75%
LICENSE-DEPENDENCIES:
  Content hash:  ff81633c53aece3489d4541bdc15ab5a5c6a8938
  License:       NOASSERTION
  Closest non-matching licenses:
    ISC similarity:         20.14%
    Zlib similarity:        19.05%
    PostgreSQL similarity:  14.43%
README.md:
  Content hash:  48a9b510f0fb871de54d6b0cb0eef7226d8bcaef
  Confidence:    90.00%
  Matcher:       Licensee::Matchers::Reference
  License:       BSD-3-Clause
  Closest non-matching licenses:
    WTFPL similarity:  5.66%
    0BSD similarity:   1.94%
    ISC similarity:    1.72%
sqlite3.gemspec:
  Confidence:  90.00%
  Matcher:     Licensee::Matchers::Gemspec
  License:     BSD-3-Clause

[flavorjones]

see #501