Fix Rubocop issues

config/application.rb

@@ -68,9 +68,11 @@ module Osem
 
     config.before_configuration do
       env_file = File.join(Rails.root, 'config', 'local_env.yml')
-      YAML.load(File.open(env_file)).each do |key, value|
-        ENV[key.to_s] = value
-      end if File.exists?(env_file)
+      if File.exist?(env_file)
+        YAML.safe_load(File.open(env_file)).each do |key, value|
+          ENV[key.to_s] = value
+        end
+      end
     end
   end
 end

config/puma.rb

@@ -46,9 +46,9 @@ end
 lowlevel_error_handler do |ex, env|
   Sentry.capture_exception(
     ex,
-    :message     => ex.message,
-    :extra       => { :puma => env },
-    :transaction => "Puma"
+    message:     ex.message,
+    extra:       { puma: env },
+    transaction: "Puma"
   )
   # note the below is just a Rack response
   [500, {}, ["An error has occurred, and engineers have been informed. Please reload the page. If you continue to have problems, contact conference@snap.berkeley.edu\n"]]

config/routes.rb

@@ -1,6 +1,6 @@
 Osem::Application.routes.draw do
 
-  mount LetterOpenerWeb::Engine, at: "/letter_opener" if Rails.env.development?
+  mount LetterOpenerWeb::Engine, at: '/letter_opener' if Rails.env.development?
 
   if ENV['OSEM_ICHAIN_ENABLED'] == 'true'
     devise_for :users, controllers: { registrations: :registrations }