Update dependency io.micrometer:micrometer-registry-prometheus to v1.8.4

Author: renovate-bot

pom.xml

@@ -149,7 +149,7 @@
         <maven-surefire-report-plugin.version>${maven-failsafe-plugin.version}</maven-surefire-report-plugin.version>
         <maven-war-plugin.version>3.3.1</maven-war-plugin.version>
         <micrometer-core.version>1.5.6</micrometer-core.version>
-        <micrometer-registry-prometheus.version>1.5.6</micrometer-registry-prometheus.version>
+        <micrometer-registry-prometheus.version>1.8.4</micrometer-registry-prometheus.version>
         <postgresql.version>42.2.18.jre7</postgresql.version>
         <selenium.version>3.13.0</selenium.version>
         <slf4j-api.version>1.7.30</slf4j-api.version>