Use go 1.11

Update go version to 1.11 in the travis pipeline and the Dockerfile.

Author: pleshakov

.travis.yml

@@ -3,7 +3,7 @@ sudo: required
 services:
 - docker
 go:
-- "1.10"
+- "1.11"
 script:
 - echo "Nginx Prometheus Exporter - commit:${TRAVIS_COMMIT}"
 - make test

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.10 as builder
+FROM golang:1.11 as builder
 ARG VERSION
 ARG GIT_COMMIT
 WORKDIR /go/src/github.com/nginxinc/nginx-prometheus-exporter