Update rails requirement from = 3.0.11 to = 6.0.0

[dependabot]

Updates the requirements on rails to permit the latest version.

Release notes

Sourced from rails's releases.

6.0.0.beta1

Active Support

• Remove deprecated Module#reachable? method.

  Rafael Mendonça França

• Remove deprecated #acronym_regex method from Inflections.

  Rafael Mendonça França

• Fix String#safe_constantize throwing a LoadError for incorrectly cased constant references.

  Keenan Brock

• Preserve key order passed to ActiveSupport::CacheStore#fetch_multi.

  fetch_multi(*names) now returns its results in the same order as the *names requested, rather than returning cache hits followed by cache misses.

  Gannon McGibbon

• If the same block is included multiple times for a Concern, an exception is no longer raised.

  Mark J. Titorenko, Vlad Bokov

• Fix bug where #to_options for ActiveSupport::HashWithIndifferentAccess
  would not act as alias for #symbolize_keys.

  Nick Weiland

• Improve the logic that detects non-autoloaded constants.

  Jan Habermann, Xavier Noria

• Deprecate ActiveSupport::Multibyte::Unicode#pack_graphemes(array) and ActiveSuppport::Multibyte::Unicode#unpack_graphemes(string)
  in favor of array.flatten.pack("U*") and string.scan(/\X/).map(&:codepoints), respectively.

  Francesco Rodríguez

• Deprecate ActiveSupport::Multibyte::Chars.consumes? in favor of String#is_utf8?.

  Francesco Rodríguez

• Fix duration being rounded to a full second.

    time = DateTime.parse("2018-1-1")
    time += 0.51.seconds
  

  Will now correctly add 0.51 second and not 1 full second.

... (truncated)

Commits

• 66cabed Preparing for 6.0.0 release
• f63df2b Merge pull request #36949 from 97jaz/thread-local-prepared-statements
• 97f9609 Highlight database.yml as code block in multiple databases guide [ci skip]
• dee31b7 Merge pull request #36946 from eugeneius/return_only_media_type_on_content_ty...
• d9aab35 Add entry about the classic autoload to the upgrading guide
• 5b327db Merge pull request #36803 from andrewkress/fix-issue-36799
• 5eaf39b Add note about human_attribute_name symbol/string
• e3b2a57 Fix attaching many uploaded files one at a time
• 5a4305f syncs autoloading guides from master [skip ci]
• ee5ee98 edits the CHANGELOG [skip ci]
• Additional commits viewable in compare view

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