fix typo

template/src/oj/problem/problem.html

@@ -39,7 +39,7 @@
                     <div class="problem-detail">{{ problem.source }}</div>
                 </div>
             {% endif %}
-            {% include "oj/problem/submit_problem.html" %}
+            {% include "oj/problem/_submit_problem.html" %}
             <div id="result">
             </div>
             <hr>