Changed RealIntervalField_class.gens() to return a tuple, modified documentation and examples accordingly

Author: CalebVL

src/sage/rings/real_mpfi.pyx

@@ -952,14 +952,14 @@ cdef class RealIntervalField_class(sage.rings.abc.RealIntervalField):
 
     def gens(self):
         """
-        Return a list of generators.
+        Return a tuple of generators.
 
         EXAMPLES::
 
             sage: RIF.gens()
-            [1]
+            (1,)
         """
-        return [self.gen()]
+        return (self.gen(),)
 
     def _is_valid_homomorphism_(self, codomain, im_gens, base_map=None):
         """