Bump to 4.2

[ocefpaf]

IPython 4.2 (April, 2016) includes various bugfixes and improvements over 4.1.

• Fix ipython -i on errors, which was broken in 4.1.
• The delay meant to highlight deprecated commands that have moved to jupyter has been removed.
• Improve compatibility with future versions of traitlets and matplotlib.
• Use stdlib shutil.get_terminal_size() to measure terminal width when displaying tracebacks (provided by - backports.shutil_get_terminal_size on Python 2).

PS: Note that I was unable to build without backports.shutil_get_terminal_size on Python 3.5 too.

Fixes https://github.com/conda-forge/ipython-feedstock/issues/1

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[ocefpaf]

Now that we have backports.shutil_get_terminal_size things are green! @pelson can you take a look and merge if you are OK with this.