Enable mutli-value checkbox in wat2wasm demo html (#1657)

Author: NateLevin1

docs/demo/wat2wasm/index.html

@@ -46,7 +46,7 @@ <h1>wat2wasm demo</h1>
     <div>
       <input type="checkbox" id="simd"><label for="simd">simd</label>
       <input type="checkbox" id="threads"><label for="threads">threads</label>
-      <input type="checkbox" id="multi_value"><label for="multi_value">multi value</label>
+      <input type="checkbox" id="multi_value" checked><label for="multi_value">multi value</label>
       <input type="checkbox" id="tail_call"><label for="tail_call">tail call</label>
       <input type="checkbox" id="bulk_memory"><label for="bulk_memory">bulk memory</label>
       <input type="checkbox" id="reference_types"><label for="reference_types">reference types</label>