Update sinatra requirement from ~> 1.4 to ~> 2.0

[dependabot-preview]

Updates the requirements on sinatra to permit the latest version.

Changelog

Sourced from sinatra's changelog.

2.0.7 / 2019-08-22

• Fix a regression #1560 by Kunpei Sakai

2.0.6 / 2019-08-21

• Fix an issue setting environment from command line option #1547, #1554 by Jordan Owens, Kunpei Sakai

• Support pandoc as a new markdown renderer #1533 by Vasiliy

• Remove outdated code for tilt 1.x #1532 by Vasiliy

• Remove an extra logic for force_encoding #1527 by Jordan Owens

• Avoid multiple errors even if params contains special values #1526 by Kunpei Sakai

• Support bundler/inline with require 'sinatra' integration #1520 by Kunpei Sakai

• Avoid TypeError when params contain a key without a value on Ruby < 2.4 #1516 by Samuel Giddins

• Improve development support and documentation and source code by Olle Jonsson, Basavanagowda Kanur, Yuki MINAMIYA

2.0.5 / 2018-12-22

• Avoid FrozenError when params contains frozen value #1506 by Kunpei Sakai

• Add support for Erubi #1494 by @tkmru

• IndifferentHash monkeypatch warning improvements #1477 by Mike Pastore

• Improve development support and documentation and source code by Anusree Prakash, Jordan Owens, @ceclinux and @krororo.

sinatra-contrib

• Add flush option to content_for #1225 by Shota Iguchi

• Drop activesupport dependency from sinatra-contrib #1448

• Update yield_content to append default to ERB template buffer #1500 by Jordan Owens

rack-protection

• Don't track the Accept-Language header by default #1504 by Artem Chistyakov

2.0.4 / 2018-09-15

• Don't blow up when passing frozen string to send_file disposition #1137 by Andrew Selder

• Fix ubygems LoadError #1436 by Pavel Rosický

... (truncated)

Commits

• 32d6833 2.0.7 release
• 3dbbd9e update CHANGELOG
• 3563a08 Merge pull request #1560 from sinatra/fix-regression
• dde8f05 fix a regression, closes #1559
• 6795b45 2.0.6 release
• 0df27f3 don't use sed. sed has difference for each platform
• 423cef3 Merge pull request #1555 from sinatra/bump-version-to-2.0.6
• 0ee9f88 bump version to 2.0.6
• dfc6d99 add v2.0.6 entry to changelog
• 95f2a18 Merge pull request #1554 from sinatra/correct-fix-1547
• Additional commits viewable in compare view

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[dependabot-preview]

A newer version of sinatra exists, but since this PR has been edited by someone other than Dependabot I haven't updated it. You'll get a PR for the updated version as normal once this PR is merged.