Typo fix

Author: cassiozen

materials/appendixA/index.html

@@ -474,7 +474,7 @@ <h1 id="loaders">Loaders</h1>
 
       <p>To exemplify, let's change our sample application and move the greeting text to a separate Json configuration file. Start by installing Webpack's json loader module:</p>
 
-      <p><pre><code class='bash'>npm install --save json-loader</code></pre></p>
+      <p><pre><code class='bash'>npm install --save-dev json-loader</code></pre></p>
 
       <p>Next, edit the webpack configuration file to add the JSON loader:</p>