Make setDescription public on RoutineInfo.Builder

Previously it was not possible to use RoutineInfo.Builder directly
to set the description.

It was possible via the Routine.Builder, but this allows users to not
care about this fact.

google-cloud-bigquery/src/main/java/com/google/cloud/bigquery/RoutineInfo.java

@@ -90,7 +90,7 @@ public abstract static class Builder {
     abstract Builder setCreationTime(Long creationMillis);
 
     /** Sets the description for the routine. */
-    abstract Builder setDescription(String description);
+    public abstract Builder setDescription(String description);
 
     abstract Builder setLastModifiedTime(Long lastModifiedMillis);