Fix sharing icons on certificate page at narrower resolutions

lms/static/certificates/sass/_layouts.scss

@@ -80,7 +80,10 @@
             margin-bottom: spacing-vertical(small);
         }
 
-        .message-actions .action {
+        .message-actions {
+            @include span(12);
+
+            .action {
                 display: block;
                 width: 100%;
                 margin: 0 auto spacing-vertical(small) auto;
@@ -104,6 +107,7 @@
                 @media(min-width: $bp-screen-md) {
                     display: inline-block;
                     vertical-align: middle;
+                    min-width: 130px;
                     width: auto;
                     margin-bottom: 0;
                     margin-right: spacing-horizontal(mid-small);
@@ -114,6 +118,7 @@
                 }
             }
         }
+    }
 }
 
 // app footer