Revert "Update dependencies"

[jml]

Reverts #1364

Looks like weaveworks/common#41 introduces a bug such that the users service now returns 404s for /metrics:

WARN: 2017/09/18 16:21:24.894355 GET /metrics (404) 196.54µs
WARN: 2017/09/18 16:21:24.894394 Is websocket request: false
GET /metrics HTTP/1.1
Host: 10.244.204.153:80
Connection: close
Accept: application/vnd.google.protobuf;proto=io.prometheus.client.MetricFamily;encoding=delimited;q=0.7,text/plain;version=0.0.4;q=0.3,*/*;q=0.1
Accept-Encoding: gzip
Authorization: Bearer REDACTED
Connection: close
User-Agent: Prometheus/1.7.1
X-Prometheus-Scrape-Timeout-Seconds: 10.000000


WARN: 2017/09/18 16:21:24.894408 Response: