doc: 2019 is the Year of the Gopher

whereas this is a longstanding tradition
and insofaras it is worth continuing such traditions
and notwithstanding an attempt at future-proofing
thetruthofthematter is that I have been waiting for years to send this change
so despiteallobjections I have updated the copyright year.

Change-Id: I55961b15a7eda35d84fdd9250afdbe19f0bf8412
Reviewed-on: https://go-review.googlesource.com/c/155928


Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>