How to update copyright years

$ npm install -t strong-tools
$ SLT_OWNER="IBM Corp." slt copyright
$ SLT_OWNER="IBM Corp." slt license
$ git commit -a -m "chore: update copyright notice years"

Since the years are determined by git commit, and this is being run at the beginning of 2018 instead of the end of 2017, the above will actually have to be run a second time (probably followed by git commit -a --amend to avoid a second commit) so that the copyright headers take in to account the start-of-year update and put 2018 in all the correct places.

The need for the SLT_OWNER env var can be removed by adding a copyright.owner property to package.json.