minor code tags syntax fix in docs

nbgrader/docs/source/user_guide/creating_and_grading_assignments.ipynb

@@ -471,7 +471,7 @@
     "\n",
     ".. note::\n",
     "\n",
-    "    Lines starting with ``### AUTOTEST`` will generate test code where the answer is visible to students. In the example above, the tests for ``squares(1)`` and ``squares(2)`` can be examined by students to see the answer. To generate test code that students can run, but where the answers are not viewable by students (they are *hashed*), begin the line with the syntax ``### HASHED AUTOTEST`` instead. You can also make `### AUTOTEST` and `### HASHED AUTOTEST` statements hidden and not runnable by students by wrapping them in ``### BEGIN HIDDEN TESTS`` and ``### END HIDDEN TESTS`` as in :ref:`autograder-tests-cell-hidden-tests`\n",
+    "    Lines starting with ``### AUTOTEST`` will generate test code where the answer is visible to students. In the example above, the tests for ``squares(1)`` and ``squares(2)`` can be examined by students to see the answer. To generate test code that students can run, but where the answers are not viewable by students (they are *hashed*), begin the line with the syntax ``### HASHED AUTOTEST`` instead. You can also make ``### AUTOTEST`` and ``### HASHED AUTOTEST`` statements hidden and not runnable by students by wrapping them in ``### BEGIN HIDDEN TESTS`` and ``### END HIDDEN TESTS`` as in :ref:`autograder-tests-cell-hidden-tests`\n",
     "    \n",
     ".. note::    \n",
     "\n",