Explicitly require some modules used in alertmanager.

Signed-off-by: Steve Simpson <[email protected]>

Author: stevesg

go.mod

@@ -20,6 +20,8 @@ require (
 	github.com/felixge/fgprof v0.9.1
 	github.com/fsouza/fake-gcs-server v1.7.0
 	github.com/go-kit/kit v0.10.0
+	github.com/go-openapi/strfmt v0.20.0
+	github.com/go-openapi/swag v0.19.14
 	github.com/go-redis/redis/v8 v8.2.3
 	github.com/gocql/gocql v0.0.0-20200526081602-cd04bd7f22a7
 	github.com/gogo/protobuf v1.3.2