fix: stop sapper complaining about unused export

Merge pull request #73 from manuel3108/fix-sapper-compiler-warning
fix sapper compiler warning
Fixes #64

Author: hperrin

packages/common/ClassAdder.svelte

@@ -6,7 +6,7 @@
 ><slot></slot></svelte:component>
 
 <script context="module">
-  export let internals = {
+  export const internals = {
     component: null,
     smuiClass: null,
     contexts: {}