Formatting of year ranges in copyright headers doesn't match Eclipse handbook

[Azquelt]

It was pointed out in the review of #543 that the year ranges in the copyright headers doesn't match the one specified in the Eclipse project handbook.

It should be 2017, 2019 whereas most of our files have 2017-2019.

[Azquelt]

Handbook has since been updated and now only requires that the earliest date that content was created to be included in the header.