Remove prompt-toolkit version pin #9
Description
I see that #8 caused us to pin the version of prompt-toolkit and that @kellyjonbrazil reported the breakage in prompt-toolkit/python-prompt-toolkit#1726 . I found that the pin makes jellex incompatible with e.g. ipython. A conflict with a common tool like ipython could hurt the adoption of jellex. Let's try and work with the most recent prompt-toolkit.