Update dependency showdown to v2

This MR contains the following updates:

Package	Type	Update	Change
showdown (source)	dependencies	major	^1.9.1 -> ^2.0.0

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Release Notes

showdownjs/showdown

v2.0.3

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Bug Fixes

• cli: fix cli to work with yargs (f8c4bd2), closes #​893

v2.0.2

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v2.0.1

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v2.0.0

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Breaking Changes

• Supported Node Versions were set to match the node release schedule which at the time of writing includes Node 12.x, 14.x, 16.x and 17.x
• The yargs dependecy was updated to ^17.2.1 to mitigate a security issue.
• The Showdown Licesnse has been changed from BSD-3-Clause to MIT

Bug Fixes

• allow escaping of colons (25c4420)
• reduce npm package size (35730b7), closes #​619

Features

• Added ellipsis option to configure if the ellipsis unicode character is used or not. ( Thanks @​VladimirV99 )
• Added a default security policy. Please report security issues to the issues tab on GitHub.

1.9.1 (2019-11-02)

Bug Fixes

• openLinksInNewWindow: add rel="noopener noreferrer" to links (1cd281f), closes #​670

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Configuration

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