Drop support for Go 1.6 (#269)
Drop support for Go 1.6 (#269)

As part of the 1.0 release, I'd really like to structure our benchmarks (and
some of our tests) using sub-tests/benchmarks. Go 1.8 is only a few weeks away
from a release, so I don't think it's too bad to drop support for 1.6 now.
uber-go/zap,uber-common/zap,uber-go/zap