Fix Rubocop offenses

config/environments/development.rb

@@ -76,7 +76,7 @@ Rails.application.configure do
   # Raises helpful error messages.
   config.assets.raise_runtime_errors = true
 
-  BetterErrors::Middleware.allow_ip! ENV['TRUSTED_IP'] if ENV['TRUSTED_IP']
+  BetterErrors::Middleware.allow_ip! ENV.fetch('TRUSTED_IP', nil) if ENV['TRUSTED_IP']
 
   # Use an evented file watcher to asynchronously detect changes in source code,
   # routes, locales, etc. This feature depends on the listen gem.

config/initializers/sentry_javascript.rb

@@ -6,7 +6,7 @@ class SentryJavascript
   end
 
   def self.dsn
-    ENV['SENTRY_JAVASCRIPT_DSN']
+    ENV.fetch('SENTRY_JAVASCRIPT_DSN', nil)
   end
 
   def self.release

config/schedule.rb

@@ -22,7 +22,7 @@
 # Learn more: http://github.com/javan/whenever
 
 set :output, "#{Whenever.path}/log/whenever/whenever_$(date +%Y%m%d%H%M%S).log"
-set :environment, ENV['RAILS_ENV'] if ENV['RAILS_ENV']
+set :environment, ENV.fetch('RAILS_ENV', nil) if ENV['RAILS_ENV']
 
 every 1.day, at: '3:00 am' do
   rake 'detect_exercise_anomalies:with_at_least[10,50]'