src/sage/structure/element.pyx: Fix placement of # optional tag

Author: Matthias Koeppe

src/sage/structure/element.pyx

@@ -1137,7 +1137,8 @@ cdef class Element(SageObject):
         We now create an ``Element`` class where we define ``_richcmp_``
         and check that comparison works::
 
-            sage: cython('''                                                # optional - sage.misc.cython
+            sage: cython(                                                   # optional - sage.misc.cython
+            ....: '''
             ....: from sage.structure.richcmp cimport rich_to_bool
             ....: from sage.structure.element cimport Element
             ....: cdef class FloatCmp(Element):