Update Rubocop to newest standards

[lodewiges]

Solves #1025

[codecov]

Codecov Report

Attention: Patch coverage is 37.50000% with 15 lines in your changes missing coverage. Please review.

Project coverage is 75.13%. Comparing base (1bd3c91) to head (493ddf3).
Report is 1 commits behind head on staging.

Files with missing lines	Patch %	Lines
app/controllers/activities_controller.rb	6.66%	14 Missing ⚠️
lib/omniauth/strategies/amber_oauth2.rb	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           staging    #1043   +/-   ##
========================================
  Coverage    75.13%   75.13%           
========================================
  Files           53       53           
  Lines         1102     1102           
========================================
  Hits           828      828           
  Misses         274      274           

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