Pub/Sub Publisher requires additional auth dependency on App Engine Standard J8

Publisher times out on App Engine Standard Java 8, work around is to include 
```
<dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>com.google.auth</groupId>
        <artifactId>google-auth-library-credentials</artifactId>
        <version>0.7.0</version>
      </dependency>
    </dependencies>
  </dependencyManagement>
```
