Start building against Micrometer 1.0.8 snapshots

See gh-15327

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

@@ -124,7 +124,7 @@
 		<logback.version>1.2.3</logback.version>
 		<lombok.version>1.16.22</lombok.version>
 		<mariadb.version>2.2.6</mariadb.version>
-		<micrometer.version>1.0.7</micrometer.version>
+		<micrometer.version>1.0.8-SNAPSHOT</micrometer.version>
 		<mockito.version>2.15.0</mockito.version>
 		<mongo-driver-reactivestreams.version>1.7.1</mongo-driver-reactivestreams.version>
 		<mongodb.version>3.6.4</mongodb.version>