Update go version to 1.7, fix vet errors

closes influxdata#1728

Author: sparrc

circle.yml

@@ -4,9 +4,9 @@ machine:
   post:
     - sudo service zookeeper stop
     - go version
-    - go version | grep 1.6.2 || sudo rm -rf /usr/local/go
-    - wget https://storage.googleapis.com/golang/go1.6.2.linux-amd64.tar.gz
-    - sudo tar -C /usr/local -xzf go1.6.2.linux-amd64.tar.gz
+    - go version | grep 1.7.1 || sudo rm -rf /usr/local/go
+    - wget https://storage.googleapis.com/golang/go1.7.1.linux-amd64.tar.gz
+    - sudo tar -C /usr/local -xzf go1.7.1.linux-amd64.tar.gz
     - go version
 
 dependencies: