package/go: bump to version 1.15.6
go1.15.6 (released 2020/12/03) includes fixes to the compiler, linker, runtime,
the go command, and the io package.
Signed-off-by: Christian Stewart <christian@paral.in>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit 267dd8b4271c72796c66d602ceb9ae1bde6cdb2a)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>