Updates sonatype endpoint. (#616)
Updates sonatype endpoint. (#616)

Migrates to new sonatype endpoint to fix continuous build.
GoogleCloudPlatform/spring-cloud-gcp,GoogleCloudPlatform/spring-cloud-gcp,GoogleCloudPlatform/spring-cloud-gcp,GoogleCloudPlatform/spring-cloud-gcp,GoogleCloudPlatform/spring-cloud-gcp