Refer to Datastore everywhere correctly by its capitalized form

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=147479683

java/google/registry/model/BackupGroupRoot.java

@@ -26,7 +26,7 @@ import javax.xml.bind.annotation.XmlTransient;
  */
 public abstract class BackupGroupRoot extends ImmutableObject {
   /**
-   * An automatically managed timestamp of when this object was last written to datastore.
+   * An automatically managed timestamp of when this object was last written to Datastore.
    *
    * <p>Note that this is distinct from the EPP-specified {@link EppResource#lastEppUpdateTime}, in
    * that this is updated on every save, rather than only in response to an {@code <update>} command