Update rack requirement from ~> 1.2 to ~> 2.1

[dependabot-preview]

Updates the requirements on rack to permit the latest version.

Changelog

Sourced from rack's changelog.

[2.1.1] - 2020-01-12

• Remove Rack::Chunked from Rack::Server default middleware. (#1475, @ioquatix)
• Restore support for code relying on SessionId#to_s. (@jeremyevans)

[2.1.0] - 2020-01-10

Added

• Add support for SameSite=None cookie value. (@hennikul)
• Add trailer headers. (@eileencodes)
• Add MIME Types for video streaming. (@styd)
• Add MIME Type for WASM. (@buildrtech)
• Add Early Hints(103) to status codes. (@egtra)
• Add Too Early(425) to status codes. (@y-yagi)
• Add Bandwidth Limit Exceeded(509) to status codes. (@CJKinni)
• Add method for custom ip_filter. (@svcastaneda)
• Add boot-time profiling capabilities to rackup. (@tenderlove)
• Add multi mapping support for X-Accel-Mappings header. (@yoshuki)
• Add sync: false option to Rack::Deflater. (Eric Wong)
• Add Builder#freeze_app to freeze application and all middleware instances. (@jeremyevans)
• Add API to extract cookies from Rack::MockResponse. (@petercline)

Changed

• Don't propagate nil values from middleware. (@ioquatix)
• Lazily initialize the response body and only buffer it if required. (@ioquatix)
• Fix deflater zlib buffer errors on empty body part. (@felixbuenemann)
• Set X-Accel-Redirect to percent-encoded path. (@diskkid)
• Remove unnecessary buffer growing when parsing multipart. (@tainoe)
• Expand the root path in Rack::Static upon initialization. (@rosenfeld)
• Make ShowExceptions work with binary data. (@axyjo)
• Use buffer string when parsing multipart requests. (@janko-m)
• Support optional UTF-8 Byte Order Mark (BOM) in config.ru. (@mikegee)
• Handle X-Forwarded-For with optional port. (@dpritchett)
• Use Time#httpdate format for Expires, as proposed by RFC 7231. (@nanaya)
• Make Utils.status_code raise an error when the status symbol is invalid instead of 500. (@adambutler)
• Rename Request::SCHEME_WHITELIST to Request::ALLOWED_SCHEMES.
• Make Multipart::Parser.get_filename accept files with + in their name. (@lucaskanashiro)
• Add Falcon to the default handler fallbacks. (@ioquatix)
• Update codebase to avoid string mutations in preparation for frozen_string_literals. (@pat)
• Change MockRequest#env_for to rely on the input optionally responding to #size instead of #length. (@janko)
• Rename Rack::File -> Rack::Files and add deprecation notice. (@postmodern).
• Prefer Base64 “strict encoding” for Base64 cookies. (@ioquatix)

Removed

• Remove to_ary from Response (@tenderlove)
• Deprecate Rack::Session::Memcache in favor of Rack::Session::Dalli from dalli gem (@fatkodima)

... (truncated)

Commits

• 799a520 Updating changelog for 2-1-stable
• 4fabf4d Bump version.
• 10512e6 Remove chunked middleware from default server stack.
• db92251 Fix ActiveStorage use-case and add test case. Fixes #1464.
• 327a865 Do not deprecate Rack::File
• 04f541b Merge pull request #1462 from jeremyevans/sessionid-to_s
• 879ae71 Merge pull request #1461 from p8/cleanup-changelog
• acf7d44 Remove changes from CHANGELOG already present in older versions [ci skip]
• 7d14bac Merge pull request #1162 from snood1205/master
• 2b61454 Merge pull request #1459 from jimeh/add-breaking-change-warning-to-changelog
• Additional commits viewable in compare view

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[dependabot-preview]

Superseded by #8.