Update build (#185)

* Update Go to 1.21.
* Update minimum Go version to 1.20.

Signed-off-by: SuperQ <[email protected]>

Author: SuperQ

.circleci/config.yml

@@ -7,7 +7,7 @@ executors:
   # also be updated.
   golang:
     docker:
-      - image: quay.io/prometheus/golang-builder:1.20-base
+      - image: quay.io/prometheus/golang-builder:1.21-base
 jobs:
   test:
     executor: golang

.promu.yml

@@ -1,13 +1,12 @@
 ---
 go:
     # This must match .circle/config.yml.
-    version: 1.20
+    version: 1.21
 repository:
     path: github.com/prometheus-community/prom-label-proxy
 build:
     binaries:
         - name: prom-label-proxy
-    flags: -tags 'netgo'
     # yamllint disable rule:line-length
     ldflags: |
         -X github.com/prometheus/common/version.Version={{.Version}}

go.mod

@@ -1,6 +1,6 @@
 module github.com/prometheus-community/prom-label-proxy
 
-go 1.19
+go 1.20
 
 require (
 	github.com/efficientgo/core v1.0.0-rc.2