Update rubocop config and setup

.rubocop.yml

@@ -1,3 +1,6 @@
+inherit_from: .rubocop_todo.yml
+require: rubocop-rspec
+
 AllCops:
   TargetRubyVersion: 2.3
 

.rubocop_todo.yml

@@ -0,0 +1,26 @@
+# This configuration was generated by
+# `rubocop --auto-gen-config`
+# on 2018-04-06 23:47:04 +0100 using RuboCop version 0.54.0.
+# The point is for the user to remove these configuration records
+# one by one as the offenses are removed from the code base.
+# Note that changes in the inspected code, or installation of new
+# versions of RuboCop, may require this file to be generated again.
+
+# Offense count: 2
+Metrics/AbcSize:
+  Max: 26
+
+# Offense count: 2
+# Configuration parameters: CountComments.
+Metrics/ClassLength:
+  Max: 132
+
+# Offense count: 2
+# Configuration parameters: CountComments.
+Metrics/MethodLength:
+  Max: 32
+
+# Offense count: 1
+Style/OptionalArguments:
+  Exclude:
+    - 'lib/bunnyrun/runner.rb'

bunnyrun.gemspec

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-lib = File.expand_path('../lib', __FILE__)
+lib = File.expand_path('lib', __dir__)
 $LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
 require 'bunnyrun/version'
 
@@ -27,6 +27,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'rake', '~> 10.0'
   spec.add_development_dependency 'rspec', '~> 3.0'
   spec.add_development_dependency 'rubocop', '~> 0.51'
+  spec.add_development_dependency 'rubocop-rspec', '~> 1.24'
 
   spec.add_runtime_dependency 'bunny', '~> 2.6'
   spec.add_runtime_dependency 'trollop', '~> 2.1.2'