Bump haml from 4.0.7 to 5.1.2 in /example/sinatra

[dependabot[bot]]

Bumps haml from 4.0.7 to 5.1.2.

Changelog

Sourced from haml's changelog.

5.1.2

Released on August 6, 2019 (diff).

• Fix crash in some environments such as New Relic by unfreezing string literals for ParseNode#inspect. #1016 (thanks Jalyna)

5.1.1

Released on May 25, 2019 (diff).

• Fix NameError bug that happens on ruby 2.6.1-2.6.3 + haml 5.1.0 + rails < 5.1 + erubi. (Akira Matsuda)

5.1.0

Released on May 16, 2019 (diff).

• Rails 6 support #1008 (thanks Seb Jacobs)
• Add escape_filter_interpolations option for backwards compatibility with haml 4 defaults #984 (thanks Will Jordan)
• Fix error on empty :javascript and :css filter blocks #986 (thanks Will Jordan)
• Respect changes in Haml::Options.defaults in Haml::TempleEngine options (Takashi Kokubun)
• Un-freeze TempleEngine precompiled string literals #983 (thanks Will Jordan)
• Various performance/memory improvements #965, #966, #963 (thanks Dillon Welch)
• Enable frozen_string_literal magic comment for all .rb files #967 (thanks Dillon Welch)

5.0.4

Released on October 13, 2017 (diff).

• Fix haml -c --stdin regression in 5.0.2. #958 (thanks Timo Göllner)
• Ruby 2.5 support (it wasn't working due to Ripper API change). (Akira Matsuda)

5.0.3

Released on September 7, 2017 (diff).

• Use String#dump instead of String#inspect to generate string literal. (Takashi Kokubun)
• Fix Erubi superclass mismatch error. #952 (thanks Robin Daugherty)

5.0.2

Released on August 1, 2017 (diff).

• Let haml -c fail if generated Ruby code is syntax error. #880 (Takashi Kokubun)
• Fix NoMethodError bug caused with Sprockets 3 and :sass filter. #930 (thanks Gonzalez Maximiliano)

... (truncated)

Commits

• 9be4e1f Version 5.1.2
• 645fcfc rails 4.2 requires bundler < 2 without bundler >= 2 being installed
• 4dbb180 Merge pull request #1016 from jalyna/fix-frozen-string-literals-on-inspect
• bc88181 Unfreeze string literals for ParseNode#inspect
• a054e2a Stop polluting toplevel unnecessarily
• 2705bbc :golf:
• c7da7a1 ruby < 1.9.3 is no longer supported
• d134875 Freeze some constants
• f7c5baa if + else = elsif
• d6c50ec This has been just an accessor since 1b784bcc50f5f437fd85b9e1a5fe147665d5a5ca
• Additional commits viewable in compare view

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