Fix icon-warning syntax error

There were a few instances of the icon-warning icon that didn't
include the file extenstion needed to when adding the file attribute
property in the icon directive.

Signed-off-by: Derick Montague <derick.montague@ibm.com>
Change-Id: Ib25c28c72285fa214f75258b0b09790d52bb6cc1
diff --git a/app/configuration/controllers/network-controller.html b/app/configuration/controllers/network-controller.html
index 0ec143c..6b4e9dd 100644
--- a/app/configuration/controllers/network-controller.html
+++ b/app/configuration/controllers/network-controller.html
@@ -121,7 +121,7 @@
     <div class="screen-reader-offscreen modal-description">Change network settings</div>
     <!-- accessibility only; used for screen readers -->
     <div class="page-header">
-      <icon file="icon-warning" aria-hidden="true"></icon><span class="accessible-text" role="alert">Warning</span>
+      <icon file="icon-warning.svg" aria-hidden="true"></icon><span class="accessible-text" role="alert">Warning</span>
       <h3 class="modal-title inline">Change network settings</h3>
     </div>
     <div class="modal__content">