docs: bump version to 1.6.0 (#336)
docs: bump version to 1.6.0 (#336)

Signed-off-by: Matt Klein <684e4e870ef5a243d6d0345280f09d95db603639@lyft.com>
lyft/envoy-api,jrajahalme/envoy-api,jrajahalme/envoy-api,lyft/envoy-api,jrajahalme/envoy-api,jrajahalme/envoy-api,lyft/envoy-api