Fix --arg format in examples.html

Author: taku0

src/examples.html

@@ -39,7 +39,7 @@ <h2>Variables and Template file</h2>
           <li>
             <x-blockcode class="example-box">
               <x-l><span class="code-comment"># command</span></x-l>
-              <x-l><span class="code-identifier">plotance</span> <span class="code-keyword">--template</span> theme.pptx <span class="code-keyword">--arg</span> <span class="code-key">year</span> 2025 <span class="code-keyword">--arg</span> <span class="code-key">month</span> 01 pageviews.md</x-l>
+              <x-l><span class="code-identifier">plotance</span> <span class="code-keyword">--template</span> theme.pptx <span class="code-keyword">--arg</span> <span class="code-key">year</span>=2025 <span class="code-keyword">--arg</span> <span class="code-key">month</span>=01 pageviews.md</x-l>
             </x-blockcode>
           </li>
         </ul>