In the md-panel directive the "open" function now returns a "mdPanelR…

…ef" wrapped in a promise. Updating externs to reflect that.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=127558022

contrib/externs/angular-material.js

@@ -863,7 +863,7 @@ md.$panel.prototype.create = function(opt_config) {};
 
 /**
  * @param {!md.$panel.config=} opt_config
- * @return {!md.$panel.MdPanelRef}
+ * @return {!angular.$q.Promise<!md.$panel.MdPanelRef>}
  */
 md.$panel.prototype.open = function(opt_config) {};