chore: update github url (#40)

Author: dwsupplee

google-cloud-datastore/pom.xml

@@ -5,7 +5,7 @@
  <version>1.102.2-SNAPSHOT</version><!-- {x-version-update:google-cloud-datastore:current} -->
  <packaging>jar</packaging>
  <name>Google Cloud Datastore</name>
- <url>https://github.com/googleapis/google-cloud-java/tree/master/google-cloud-clients/google-cloud-datastore</url>
+ <url>https://github.com/googleapis/java-datastore</url>
  <description>
  Java idiomatic client for Google Cloud Datastore.
  </description>