Upgrade to prometheus 0.13

Author: shepmaster

ui/Cargo.lock

@@ -29,7 +29,7 @@ router = "0.6.0"
 openssl-probe = "0.1.2"
 dotenv = "0.15.0"
 snafu = "0.6.0"
-prometheus = "0.12.0"
+prometheus = "0.13.0"
 strum = { version = "0.22.0", features = ["derive"] }
 
 [dependencies.playground-middleware]