upgrade prometheus_exporter

Author: flearc

sentinel-core/Cargo.toml

@@ -54,7 +54,7 @@ env_logger = { version = "0.10.0", optional = true }
 log4rs = { version = "1", optional = true }
 log = "0.4"
 regex = { version = "1.5", optional = true }
-prometheus_exporter = { version = "0.8.4", optional = true }
+prometheus_exporter = { version = "0.8.5", optional = true }
 # todo: simplify encapsulation
 # using getset = "0.1.1"
 lru = "0.7.5"