Fixes undefining client_method when set to the same client_method

Issue zipmark#167

features/redefining_same_client.feature

@@ -0,0 +1,33 @@
+Feature: Redefining the client method to the same method
+  Background:
+    Given a file named "app.rb" with:
+      """
+      class App
+        def self.call(env)
+          [200, {}, ["Hello, world"]]
+        end
+      end
+      """
+    And a file named "app_spec.rb" with:
+      """
+      require "rspec_api_documentation"
+      require "rspec_api_documentation/dsl"
+
+      RspecApiDocumentation.configure do |config|
+        config.app = App
+        config.client_method = :client
+      end
+
+      resource "Example Request" do
+        get "/" do
+          example_request "Trying out get" do
+            expect(status).to eq(200)
+          end
+        end
+      end
+      """
+    When  I run `rspec app_spec.rb --require ./app.rb --format RspecApiDocumentation::ApiFormatter`
+
+  Scenario: Output should have the correct error line
+    Then  the output should contain "1 example, 0 failures"
+    And   the exit status should be 0

lib/rspec_api_documentation/configuration.rb

@@ -119,6 +119,8 @@ def self.add_setting(name, opts = {})
     }
 
     def client_method=(new_client_method)
+      return if new_client_method == client_method
+
       RspecApiDocumentation::DSL::Resource.module_eval <<-RUBY
         alias :#{new_client_method} #{client_method}
         undef #{client_method}