[fix] remove redundant spaces (sveltejs#209)

Removed redundant whitespaces to make it consistent with `app-a` and docs code style in general

Author: timnikolsky

content/tutorial/01-svelte/06-bindings/03-checkbox-inputs/app-b/src/lib/App.svelte

@@ -19,4 +19,4 @@
 	</p>
 {/if}
 
-<button disabled={!yes}> Subscribe </button>
+<button disabled={!yes}>Subscribe</button>