fix(b-toaster): CSS fix for IE11 support (fixes #3327) (#3328)

Adds in css `width: 100%` for IE11 positioning.

Author: tmorehouse

src/components/toast/_toaster.scss

@@ -46,6 +46,7 @@
     .b-toaster-slot {
       position: absolute;
       max-width: $toast-max-width;
+      width: 100%; /* IE11 fix */
       left: 0;
       right: 0;
       padding: 0;