Fix formatting in overview.rst (ipython#14999)

Code block broke bulleted list

Author: krassowski

docs/source/overview.rst

@@ -169,19 +169,18 @@ Main features of the interactive shell
   intelligent enough to do more repetitions for commands that finish very
   quickly in order to get a better estimate of their running time. 
 
-.. sourcecode:: ipython
+  .. sourcecode:: ipython
 
     In [1]: %timeit 1+1
     7.88 ns ± 0.0494 ns per loop (mean ± std. dev. of 7 runs, 100000000 loops each)
 
     In [2]: %timeit [math.sin(x) for x in range(5000)]
     608 µs ± 5.57 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)
 
-.. 
+  .. 
 
   To get the timing information for more than one expression, use the
   :samp:`%%timeit` cell magic command.
-  
 
 * Doctest support. The special :samp:`%doctest_mode` command toggles a mode
   to use doctest-compatible prompts, so you can use IPython sessions as