Hardcode year for copyright headers

[liry]

Not to break builds at the New Year

[gdgate]

Build succeeded (check pipeline).

[gdgate]

Build succeeded (gate pipeline).

• https://checklist.intgdc.com/job/compliance/job/gooddata-java-merge-compliance-check/305/ : SUCCESS in 19s
• https://checklist.intgdc.com/job/compliance/job/gooddata-java-fossa-scanning-zuul/3/ : SUCCESS in 2m 17s (non-voting)