Fix link to azure-spring-boot-metrics-starter (#668)

The link was broken because there is no Readme file present in azure-spring-boot-metrics-starter. This change points the link at the directory instead.

Fixes #513

README.md

@@ -33,7 +33,7 @@ Starter Name | Version for Spring Boot 2.1.x | Version for Spring Boot 2.0.x
 [azure-mediaservices-spring-boot-starter](azure-spring-boot-starters/azure-mediaservices-spring-boot-starter/README.md) | [![Maven Central](https://img.shields.io/maven-central/v/com.microsoft.azure/azure-mediaservices-spring-boot-starter.svg)](http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22com.microsoft.azure%22%20AND%20a%3A%22azure-mediaservices-spring-boot-starter%22) | [![](https://img.shields.io/maven-central/v/com.microsoft.azure/azure-mediaservices-spring-boot-starter/2.0.svg)](https://search.maven.org/search?q=g:com.microsoft.azure%20AND%20a:azure-mediaservices-spring-boot-starter%20AND%20v:2.0.*)
 [azure-servicebus-spring-boot-starter](azure-spring-boot-starters/azure-servicebus-spring-boot-starter/README.md) | [![Maven Central](https://img.shields.io/maven-central/v/com.microsoft.azure/azure-servicebus-spring-boot-starter.svg)](http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22com.microsoft.azure%22%20AND%20a%3A%22azure-servicebus-spring-boot-starter%22) | [![](https://img.shields.io/maven-central/v/com.microsoft.azure/azure-servicebus-spring-boot-starter/2.0.svg)](https://search.maven.org/search?q=g:com.microsoft.azure%20AND%20a:azure-servicebus-spring-boot-starter%20AND%20v:2.0.*)
 [spring-data-gremlin-boot-starter](azure-spring-boot-starters/spring-data-gremlin-boot-starter/README.md) | [![Maven Central](https://img.shields.io/maven-central/v/com.microsoft.azure/spring-data-gremlin-boot-starter.svg)](http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22com.microsoft.azure%22%20AND%20a%3A%22spring-data-gremlin-boot-starter%22) | [![](https://img.shields.io/maven-central/v/com.microsoft.azure/spring-data-gremlin-boot-starter/2.0.svg)](https://search.maven.org/search?q=g:com.microsoft.azure%20AND%20a:spring-data-gremlin-boot-starter%20AND%20v:2.0.*)
-[azure-spring-boot-metrics-starter](azure-spring-boot-starters/azure-spring-boot-metrics-starter/README.md) | [![Maven Central](https://img.shields.io/maven-central/v/com.microsoft.azure/azure-spring-boot-metrics-starter.svg)](http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22com.microsoft.azure%22%20AND%20a%3A%22azure-spring-boot-metrics-starter%22) | [![](https://img.shields.io/maven-central/v/com.microsoft.azure/azure-spring-boot-metrics-starter/2.0.svg)](https://search.maven.org/search?q=g:com.microsoft.azure%20AND%20a:azure-spring-boot-metrics-starter%20AND%20v:2.0.*)
+[azure-spring-boot-metrics-starter](azure-spring-boot-starters/azure-spring-boot-metrics-starter) | [![Maven Central](https://img.shields.io/maven-central/v/com.microsoft.azure/azure-spring-boot-metrics-starter.svg)](http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22com.microsoft.azure%22%20AND%20a%3A%22azure-spring-boot-metrics-starter%22) | [![](https://img.shields.io/maven-central/v/com.microsoft.azure/azure-spring-boot-metrics-starter/2.0.svg)](https://search.maven.org/search?q=g:com.microsoft.azure%20AND%20a:azure-spring-boot-metrics-starter%20AND%20v:2.0.*)
 
 ### Snapshots  
 [![Nexus OSS](https://img.shields.io/nexus/snapshots/https/oss.sonatype.org/com.microsoft.azure/azure-spring-boot.svg)](https://oss.sonatype.org/content/repositories/snapshots/com/microsoft/azure/azure-spring-boot/)