Move last refresh time format to 'medium'

From https://docs.angularjs.org/api/ng/filter/date:
"'medium': equivalent to 'MMM d, y h:mm:ss a' for en_US locale
(e.g. Sep 3, 2010 12:05:08 PM)"
This is a similar format as to what was present on the GUI
before for en_US.
Letting the browser choose the format, is important.
Still displayed in user's timezone.

Before: 1:52:11 May 01 2018
After: May 1, 2018 1:52:11 PM

Change-Id: Iff2769a22125b1ea4f6f375a6b2b6866438149c5
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/app/common/directives/app-header.html b/app/common/directives/app-header.html
index 5395d2a..e396537 100644
--- a/app/common/directives/app-header.html
+++ b/app/common/directives/app-header.html
@@ -19,7 +19,7 @@
 				<i class="icon icon-angle" aria-hidden="true"></i><span ng-class="{'status-light__error': dataService.server_health == 'Critical', 'status-light__warn': dataService.server_health == 'Warning', 'status-light__good': dataService.server_health == 'Good'}">{{dataService.server_health}}</span></a>
 			 <a href="#/server-control/power-operations" class="header__server-power" role="button">Server power
 				<i class="icon icon-angle" aria-hidden="true"></i><span ng-class="{'status-light__off': dataService.server_state == 'Off', 'status-light__disabled': dataService.server_state == 'Unreachable', 'status-light__good': dataService.server_state == 'Running', 'status-light__error': dataService.server_state == 'Quiesced'}">{{dataService.server_state | quiescedToError}}</span></a>
-			<p class="header__refresh">Data last refreshed<span>{{dataService.last_updated |date:'h:mm:ss MMM dd yyyy'}}</span>
+			<p class="header__refresh">Data last refreshed<span>{{dataService.last_updated | date:'medium'}}</span>
 			</p>
 			<button class="header__page-refresh" ng-click="refresh()" aria-label="refresh page data">
 				<span>Refresh</span>