Fix wrong CSS class

Author: acsany

code-image-generator/source_code_final/templates/image.html

@@ -5,7 +5,7 @@
 {% block content %}
 <form>
   {% if image_b64 %}
-    <div class="code_picture">
+    <div class="code-picture">
       <img src="data:image/png;base64,{{ image_b64 | safe }}"
            alt="Code Image" />
     </div>

code-image-generator/source_code_step_04/templates/image.html

@@ -5,7 +5,7 @@
 {% block content %}
 <form>
   {% if image_b64 %}
-    <div class="code_picture">
+    <div class="code-picture">
       <img src="data:image/png;base64,{{ image_b64 | safe }}"
            alt="Code Image" />
     </div>