Update Golang to 1.12.1 (elastic#11330)

Changes in 1.12: https://golang.org/doc/go1.12
Changes in minor release: https://github.com/golang/go/issues?q=milestone%3AGo1.12.1

Updated vendored packages:
- `github.com/tsg/gopacket/pcap`
- `github.com/docker/docker/pkg/*`
- `github.com/docker/go-connections`

New vendored packages (as required by dependencies):
- `github.com/konsorten/go-windows-terminal-sequences`

Removed vendored package:
- `github.com/Sirupsen/logrus`: `github.com/sirupsen/logrus` is used and it leads to a case insensitive collision, required by docker dependencies

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.11.5
+FROM golang:1.12.1
 MAINTAINER Noémi Ványi <noemi.vanyi@elastic.co>
 
 RUN set -x && \