DOC: Updated links to 2 tutorials in tutorials.rst
Two of the links to the [pandas-cookbook](https://github.com/jvns/pandas-cookbook) did not work for version `v0.2` of the documents. Now all links work. Where a version  `v0.2` exists, it links to that version. In the remaining two cases, it now links to version `v0.1` instead of raising the `404: Page not found` error.