PLT-3202 Re-render timestamps when display settings switch between 12h and 24h (#3337)

* Made post timestamp switch from 12h to 24h without refreshing

* Made RHS post timestamps switch from 12h to 24h without refreshing

webapp/components/rhs_comment.jsx

@@ -38,6 +38,11 @@ export default class RhsComment extends React.Component {
         if (nextProps.compactDisplay !== this.props.compactDisplay) {
             return true;
         }
+
+        if (nextProps.useMilitaryTime !== this.props.useMilitaryTime) {
+            return true;
+        }
+
         if (!Utils.areObjectsEqual(nextProps.post, this.props.post)) {
             return true;
         }
@@ -231,7 +236,7 @@ export default class RhsComment extends React.Component {
                                         day='numeric'
                                         month='long'
                                         year='numeric'
-                                        hour12={!Utils.isMilitaryTime()}
+                                        hour12={!this.props.useMilitaryTime}
                                         hour='2-digit'
                                         minute='2-digit'
                                     />
@@ -259,5 +264,6 @@ RhsComment.propTypes = {
     post: React.PropTypes.object,
     user: React.PropTypes.object.isRequired,
     currentUser: React.PropTypes.object.isRequired,
-    compactDisplay: React.PropTypes.bool
+    compactDisplay: React.PropTypes.bool,
+    useMilitaryTime: React.PropTypes.bool.isRequired
 };