Fix property being passed to lit element

Change-Id: Ib9d13e36a470cf0b03b1c38ccb0707f8c966ac85
diff --git a/polygerrit-ui/app/elements/change-list/gr-user-header/gr-user-header.ts b/polygerrit-ui/app/elements/change-list/gr-user-header/gr-user-header.ts
index e87b4f9..05b5390 100644
--- a/polygerrit-ui/app/elements/change-list/gr-user-header/gr-user-header.ts
+++ b/polygerrit-ui/app/elements/change-list/gr-user-header/gr-user-header.ts
@@ -85,7 +85,7 @@
         <div>
           <span>Joined:</span>
           <gr-date-formatter
-            date-str="${this._computeDetail(
+            dateStr="${this._computeDetail(
               this._accountDetails,
               'registered_on'
             )}"