Merge pull request #238 from sdurrheimer/fix-circleci-flanky-go-get

Fix CircleCI flanky go get

circle.yml

@@ -2,7 +2,7 @@ machine:
   environment:
     DOCKER_IMAGE_NAME: prom/node-exporter
     QUAY_IMAGE_NAME: quay.io/prometheus/node-exporter
-    DOCKER_TEST_IMAGE_NAME: quay.io/prometheus/golang-builder:1.5.4-main
+    DOCKER_TEST_IMAGE_NAME: quay.io/prometheus/golang-builder:1.6.2-main
     REPO_PATH: github.com/prometheus/node_exporter
   pre:
     - sudo curl -L -o /usr/bin/docker 'https://s3-external-1.amazonaws.com/circle-downloads/docker-1.9.1-circleci'
@@ -13,7 +13,7 @@ machine:
 
 dependencies:
   pre:
-    - go get -u github.com/prometheus/promu
+    - make promu
     - docker info
   override:
     - promu crossbuild