Sync Parallel Letter Frequency tests with canonical specs

[antoine-duchenet]

Hi !

I updated the tests to match the problem specifications.
A minor update of the @reject_characters RegExp in the example implementation was needed to pass the new tests.

Relates to #1027 .

[jiegillet]

This is great, thanks for doing it!
I only have a small request, could you format the @dostoevsky strings with triple quotes:

@dostoevsky [
  """"
  I am a sick man.... I am a spiteful man. I am an unattractive man.
  I believe my liver is diseased. However, I know nothing at all about my disease, and do not
  [....]
  """,
  """
  Gentlemen, I am joking, and I know myself that my jokes are not brilliant
  [...]
  """
  ]

And I think it's fine not to worry about an extra newline here or there in this case :)

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[antoine-duchenet]

This is great, thanks for doing it! I only have a small request, could you format the @dostoevsky strings with triple quotes:

Done !

[jiegillet]

Very nice, thank you!