Fix import error

Signed-off-by: Felix Yuan <[email protected]>

Author: Sticksman

go.mod

@@ -7,6 +7,7 @@ require (
 	github.com/alecthomas/kingpin/v2 v2.4.0
 	github.com/lib/pq v1.10.9
 	github.com/prometheus/client_golang v1.20.4
+	github.com/prometheus/client_model v0.6.1
 	github.com/prometheus/common v0.60.0
 	github.com/prometheus/exporter-toolkit v0.13.0
 	github.com/smartystreets/goconvey v1.8.1
@@ -25,7 +26,6 @@ require (
 	github.com/mdlayher/vsock v1.2.1 // indirect
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
 	github.com/mwitkow/go-conntrack v0.0.0-20190716064945-2f068394615f // indirect
-	github.com/prometheus/client_model v0.6.1 // indirect
 	github.com/prometheus/procfs v0.15.1 // indirect
 	github.com/smarty/assertions v1.15.0 // indirect
 	github.com/xhit/go-str2duration/v2 v2.1.0 // indirect