Set minimum version for go to 1.16 (prometheus#372)

Signed-off-by: Manuel Rüger <manuel@rueg.eu>

Author: mrueg

.circleci/config.yml

@@ -91,7 +91,6 @@ workflows:
           matrix:
             parameters:
               go_version:
-                - "1.15"
                 - "1.16"
                 - "1.17"
       - test-assets:

go.mod

@@ -14,4 +14,4 @@ require (
 	gopkg.in/yaml.v2 v2.4.0
 )
 
-go 1.15
+go 1.16

sigv4/go.mod

@@ -1,11 +1,11 @@
 module github.com/prometheus/common/sigv4
 
-go 1.15
-
 require (
 	github.com/aws/aws-sdk-go v1.43.26
 	github.com/prometheus/client_golang v1.12.1
 	github.com/prometheus/common v0.32.1
 	github.com/stretchr/testify v1.7.1
 	gopkg.in/yaml.v2 v2.4.0
 )
+
+go 1.16