Fix ipython directive error by adding blank lines after directives in tutorial.rst (GH#648)

[Aniketsy]

This PR fixes the Sphinx error:
"maximum 4 argument(s) allowed, 17 supplied"
by ensuring a blank line is present after each .. ipython:: python directive in tutorial.rst.

[coveralls]

coverage: 94.978%. remained the same
when pulling 2ca49fd on Aniketsy:fix-ipython-blank-line
into 04a130e on data-8:master.

[adnanhemani]

I'm getting the following error after applying this fix:

(base) Adnans-MacBook-Pro:datascience ahemani$ make docs
cd docs ; make html
mkdir -p _build/html/_images
sphinx-build -b html -d _build/doctrees   . _build/html
Running Sphinx v5.3.0
WARNING: Invalid configuration value found: 'language = None'. Update your configuration to a valid language code. Falling back to 'en' (English).
WARNING: The config value `ipython_mplbackend' has type `NoneType', defaults to `str'.
loading pickled environment... done
[autosummary] generating autosummary for: _autosummary/datascience.tables.Table.__init__.rst, _autosummary/datascience.tables.Table.append.rst, _autosummary/datascience.tables.Table.append_column.rst, _autosummary/datascience.tables.Table.apply.rst, _autosummary/datascience.tables.Table.as_html.rst, _autosummary/datascience.tables.Table.as_text.rst, _autosummary/datascience.tables.Table.bar.rst, _autosummary/datascience.tables.Table.barh.rst, _autosummary/datascience.tables.Table.bin.rst, _autosummary/datascience.tables.Table.boxplot.rst, ..., _autosummary/datascience.tables.Table.with_row.rst, _autosummary/datascience.tables.Table.with_rows.rst, formats.rst, index.rst, maps.rst, predicates.rst, reference-nb/datascience-reference.ipynb, tables.rst, tutorial.rst, util.rst
building [mo]: targets for 0 po files that are out of date
building [html]: targets for 1 source files that are out of date
updating environment: 0 added, 1 changed, 0 removed
reading sources... [100%] tutorial                                                                                
Exception occurred:
  File "/Users/ahemani/anaconda3/lib/python3.7/site-packages/IPython/sphinxext/ipython_directive.py", line 1030, in run
    raise RuntimeError(message)
RuntimeError: Code input with no code at /Users/ahemani/Development/data8/datascience/docs/tutorial.rst, line 436
The full traceback has been saved in /var/folders/cy/4xhmk_g91jdd4tv63yt_7x4r0000gn/T/sphinx-err-kd28k7rd.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!
make[1]: *** [html] Error 2
make: *** [docs] Error 2

But at a bare minimum, this change seems to be in the right direction. I will approve and merge and we can see what the next steps are from there.