Add link to Maven Central for maven-central badge. (#1468)

Used to link to the image, which wasn't super useful.

README.md

@@ -5,7 +5,7 @@ Java idiomatic client for [Google Cloud Platform][cloud-platform] services.
 
 [![Build Status](https://travis-ci.org/GoogleCloudPlatform/google-cloud-java.svg?branch=master)](https://travis-ci.org/GoogleCloudPlatform/google-cloud-java)
 [![Coverage Status](https://coveralls.io/repos/GoogleCloudPlatform/google-cloud-java/badge.svg?branch=master)](https://coveralls.io/r/GoogleCloudPlatform/google-cloud-java?branch=master)
-[![Maven](https://img.shields.io/maven-central/v/com.google.cloud/google-cloud.svg)]( https://img.shields.io/maven-central/v/com.google.cloud/google-cloud.svg)
+[![Maven](https://img.shields.io/maven-central/v/com.google.cloud/google-cloud.svg)](http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22com.google.cloud%22%20a%3A%22google-cloud%22)
 [![Codacy Badge](https://api.codacy.com/project/badge/grade/9da006ad7c3a4fe1abd142e77c003917)](https://www.codacy.com/app/mziccard/google-cloud-java)
 [![Dependency Status](https://www.versioneye.com/user/projects/56bd8ee72a29ed002d2b0969/badge.svg?style=flat)](https://www.versioneye.com/user/projects/56bd8ee72a29ed002d2b0969)