Merge pull request #2864 from snowflakeOps/2.3

use a better and smaller image for open graph (e.g for slack)

Author: jbrooksuk

public/img/ogimage.png

@@ -19,7 +19,7 @@
 
     <meta property="og:type" content="website">
     <meta property="og:title" content="{{ $site_title }}">
-    <meta property="og:image" content="/img/favicon.png">
+    <meta property="og:image" content="/img/ogimage.png">
     <meta property="og:description" content="{{ trans('cachet.description', ['app' => $app_name]) }}">
 
     <!-- Mobile IE allows us to activate ClearType technology for smoothing fonts for easy reading -->