Upgrade to micrometer 1.0.0-rc.8

Closes gh-11575

Author: philwebb

spring-boot-project/spring-boot-dependencies/pom.xml

@@ -112,7 +112,7 @@
 		<logback.version>1.2.3</logback.version>
 		<lombok.version>1.16.20</lombok.version>
 		<mariadb.version>2.2.1</mariadb.version>
-		<micrometer.version>1.0.0-SNAPSHOT</micrometer.version>
+		<micrometer.version>1.0.0-rc.8</micrometer.version>
 		<mssql-jdbc.version>6.2.2.jre8</mssql-jdbc.version>
 		<mockito.version>2.13.0</mockito.version>
 		<mongo-driver-reactivestreams.version>1.7.0</mongo-driver-reactivestreams.version>