Append dashboard url with slash to improve user experience

The Dashboard url in LMS is only accessible in the absence of
slash at its end.To improve the user experience its URL is
updated.

LEARNER-3812

lms/urls.py

@@ -60,7 +60,7 @@ urlpatterns = [
 
     url(r'', include('student.urls')),
     # TODO: Move lms specific student views out of common code
-    url(r'^dashboard$', student_views.dashboard, name='dashboard'),
+    url(r'^dashboard/?$', student_views.dashboard, name='dashboard'),
     url(r'^change_enrollment$', student_views.change_enrollment, name='change_enrollment'),
 
     # Event tracking endpoints