Bump github.com/prometheus/alertmanager in /adapter (#233)

Bumps [github.com/prometheus/alertmanager](https://github.com/prometheus/alertmanager) from 0.20.0 to 0.25.1.
- [Release notes](https://github.com/prometheus/alertmanager/releases)
- [Changelog](https://github.com/prometheus/alertmanager/blob/v0.25.1/CHANGELOG.md)
- [Commits](prometheus/alertmanager@v0.20.0...v0.25.1)

---
updated-dependencies:
- dependency-name: github.com/prometheus/alertmanager
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

adapter/go.mod

@@ -5,10 +5,10 @@ go 1.13
 require (
 	github.com/emicklei/go-restful v2.16.0+incompatible
 	github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b
-	github.com/json-iterator/go v1.1.10
-	github.com/prometheus/alertmanager v0.20.0
-	github.com/prometheus/common v0.7.0
+	github.com/json-iterator/go v1.1.12
+	github.com/prometheus/alertmanager v0.25.1
+	github.com/prometheus/common v0.38.0
 	github.com/spf13/cobra v0.0.5
 	github.com/spf13/pflag v1.0.5
-	golang.org/x/text v0.3.8
+	golang.org/x/text v0.5.0
 )