Update Go dependencies

This includes go-jira v1.15.0 supporting Personal Access Tokens (PATs).

go.mod

@@ -3,15 +3,11 @@ module github.com/prometheus-community/jiralert
 go 1.14
 
 require (
-	github.com/andygrunwald/go-jira v1.11.2-0.20200514151831-146229d2ab58
-	github.com/fatih/structs v1.1.0 // indirect
-	github.com/go-kit/kit v0.10.0
-	github.com/golang/protobuf v1.4.1 // indirect
-	github.com/google/go-querystring v1.0.0 // indirect
+	github.com/andygrunwald/go-jira v1.15.0
+	github.com/go-kit/kit v0.12.0
 	github.com/pkg/errors v0.9.1
-	github.com/prometheus/client_golang v1.6.0
-	github.com/prometheus/common v0.10.0 // indirect
-	github.com/stretchr/testify v1.5.1
+	github.com/prometheus/client_golang v1.12.1
+	github.com/stretchr/testify v1.7.0
 	github.com/trivago/tgo v1.0.7
-	gopkg.in/yaml.v2 v2.3.0
+	gopkg.in/yaml.v2 v2.4.0
 )