EDUCATOR-1685 Fix for tex2jax \tag{} width issue

This prevents the library from applying an inline style that is much
too wide and breaks everything.

lms/static/sass/discussion/_mixins.scss

@@ -75,6 +75,10 @@
     @include padding-left($baseline*2);
     @include padding-right(0);
   }
+
+  svg {
+    max-width: 100%;
+  }
 }
 
 @-webkit-keyframes fadeIn {