Fix RuboCop 0.50 errors

Closes GH-158

Please note that Performance/HashEachMethods was a false positive.

.rubocop.yml

@@ -2,6 +2,11 @@ inherit_from:
   - .rubocop_todo.yml
   - .rubocop_dnsimple.yml
 
+AllCops:
+  Exclude:
+    - '*.gemspec'
+    - 'Rakefile'
+
 # [codesmell]
 # It's irrelevant here, but it could be a code smell.
 # Hence keep it disabled, but don't include it in the DNSimple suite.

.rubocop_dnsimple.yml

@@ -84,6 +84,13 @@ Metrics/ParameterLists:
 Metrics/PerceivedComplexity:
   Enabled: false
 
+# We use it from time to time, as it's not always possible (or maintainable)
+# to use simple ? methods.
+# Moreover, it's actually more efficient to not-use predicates:
+# https://github.com/bbatsov/rubocop/issues/3633
+Naming/PredicateName:
+  Enabled: false
+
 # [codesmell]
 # I don't really get the point of this cop.
 Performance/RedundantMerge:
@@ -175,13 +182,6 @@ Style/NumericLiterals:
 Style/PercentLiteralDelimiters:
   Enabled: false
 
-# We use it from time to time, as it's not always possible (or maintainable)
-# to use simple ? methods.
-# Moreover, it's actually more efficient to not-use predicates:
-# https://github.com/bbatsov/rubocop/issues/3633
-Style/PredicateName:
-  Enabled: false
-
 # Do we care?
 Style/RegexpLiteral:
   Enabled: false

lib/dnsimple/client.rb

@@ -61,7 +61,7 @@ def self.versioned(path)
     def initialize(options = {})
       defaults = Dnsimple::Default.options
 
-      Dnsimple::Default.keys.each do |key|
+      Dnsimple::Default.keys.each do |key| # rubocop:disable Performance/HashEachMethods
         instance_variable_set(:"@#{key}", options[key] || defaults[key])
       end
 

lib/dnsimple/struct/extended_attribute.rb

@@ -24,7 +24,7 @@ class Option < Base
       attr_accessor :required
 
       # @return [Array<Options>] The array of options with possible values for the extended attribute
-      attr_accessor :options
+      attr_reader :options
 
       def initialize(*)
         super

lib/dnsimple/struct/service.rb

@@ -45,7 +45,7 @@ class Setting < Base
       attr_accessor :default_subdomain
 
       # @return [Array<Settings>] The array of settings to setup this service, if setup is required.
-      attr_accessor :settings
+      attr_reader :settings
 
       def initialize(*)
         super

lib/dnsimple/struct/whoami.rb

@@ -3,10 +3,10 @@ module Struct
 
     class Whoami < Base
       # @return [Account] The account, if present.
-      attr_accessor :account
+      attr_reader :account
 
       # @return [String] The user, if present.
-      attr_accessor :user
+      attr_reader :user
 
 
       # Converts account to a Struct::Account and sets it.