Update prompt-toolkit requirement from <2.0.0,>=0.57 to >=0.57,<3.0.0

[dependabot-preview]

Updates the requirements on prompt-toolkit to permit the latest version.

Changelog

Sourced from prompt-toolkit's changelog.

2.0.4: 2018-07-22

Bug fixes:

• Fix render height for rendering full screen applications in Windows.
• Fix in TextArea. Set accept_handler to None if not given.
• Go to the beginning of the next line when enter is pressed in Vi navigation
  mode, and the buffer doesn't have an accept handler.
• Fix the default argument of the prompt function when called multiple
  times.
• Display decomposed multiwidth characters correctly.
• Accept history in prompt() function again.

Backwards incompatible changes:

• Renamed PipeInput to PosixPipeInput. Added Win32PipeInput and
  create_input_pipe.
• Pass buffer argument to the accept_handler of TextArea.

New features:

• Added accept_default argument to prompt().
• Make it easier to change the body/title of a Frame/Dialog.
• Added DynamicContainer.
• Added merge_completers for merging multiple completers together.
• Add vt100 data to key presses in Windows.
• Handle left/right key bindings in Vi block insert mode.

2.0.3: 2018-06-08

Bug fixes:

• Fix in 'x' and 'X' Vi key bindings. Correctly handle line endings and args.
• Fixed off by one error in Vi line selection.
• Fixed bugs in Vi block selection. Correctly handle lines that the selection
  doesn't cross.
• Python 2 bugfix. Handle str/unicode correctly.
• Handle option+left/right in iTerm.

2.0.2: 2018-06-03

Bug fixes:

• Python 3.7 support: correctly handle StopIteration in asynchronous generator.
• Fixed off-by-one bug in Vi visual block mode.
• Bugfix in TabsProcessor: handle situations when the cursor is at the end of
  the line.

2.0.1: 2018-06-02

... (truncated)

Commits

• See full diff in compare view

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[otavio]

@chtavares592 this is good to have this update however it needs minor changes in the source code to be able to be merged, as you can see in the Travis log. Please take a look.

[otavio]

Please fix those minor issues.