Update the Copyright year to 2018.

[carlosalberto]

Preparing the merge of v0.31.0 into master prior to the release, I came with the need to update the Copyright year for the merged files. So a choice is to do a full pass once, or else do it manually, as we go.

Opinions?

[coveralls]

Coverage remained the same at 82.63% when pulling a671090060fefe5eeb10ed0932588ea0eb3a3fac on carlosalberto:update_copyright_year into 91d4ff7bd3e6b9aa8bc362d06455b7bdf58c0c8a on opentracing:v0.31.0.

[yurishkuro]

once is better (less overhead), although technically incorrect

[coveralls]

Coverage remained the same at 82.63% when pulling c86728850b194fd7c80152f91dab3e83503004e2 on carlosalberto:update_copyright_year into 91d4ff7bd3e6b9aa8bc362d06455b7bdf58c0c8a on opentracing:v0.31.0.

[carlosalberto]

Forgot to mention this will cover #239

[malafeev]

am I right that there is no automatic check of copyright year during the build? I don't see that license.git.copyrightYears is set (src/etc/header.txt).

[pavolloffay]

@malafeev a year should be derived from the git history

[pavolloffay]

There is also section in release.md https://github.com/opentracing/opentracing-java/blob/master/RELEASE.md#first-release-of-the-year

[malafeev]

thanks @pavolloffay