Fix #increment! and #decrement! methods to behave similarly to the Rails' ActiveRecord methods

[andrykonchin]

Changes:

• #increment!/#decrement!:
  • returns self, not boolean
  • saves only the attribute new value, not other modified attributes
  • skips callbacks and validation
  • does not reload a model
  • support a :touch option (similar to the Rails' increment! and #decrement! methods that is described here)
• .inc
  • support the :touch option similar to the equivalent Rails' method .update_counters
• fix CI for Ruby 2.3-2.5 and use default RubyGems and Bundler versions (see https://github.com/ruby/setup-ruby/issues/441)

Related links:

• https://api.rubyonrails.org/classes/ActiveRecord/Persistence.html#method-i-decrement-21
• https://api.rubyonrails.org/classes/ActiveRecord/Persistence.html#method-i-increment-21
• https://api.rubyonrails.org/classes/ActiveRecord/CounterCache/ClassMethods.html#method-i-update_counters

[codecov[bot]]

Codecov Report

Merging #624 (f423a3d) into master (6e2b56b) will increase coverage by 0.09%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #624      +/-   ##
==========================================
+ Coverage   90.06%   90.15%   +0.09%     
==========================================
  Files          59       60       +1     
  Lines        3020     3048      +28     
==========================================
+ Hits         2720     2748      +28     
  Misses        300      300              

Impacted Files	Coverage Δ
lib/dynamoid/persistence.rb	98.07% <100.00%> (-0.10%)	:arrow_down:
lib/dynamoid/persistence/inc.rb	100.00% <100.00%> (ø)

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[github-actions[bot]]

Package	Line Rate	Health
dynamoid	90%	➖
Summary	90% (2748 / 3048)	➖

Minimum allowed line rate is 90%