Move OpenAPI spec from spec/ to openapi/

Naming a directory `spec` in a Ruby project is terribly ambiguous. This
clarifies the purpose of this directory and makes it easier to find if
you know that you're looking for OpenAPI.

README.md

@@ -142,7 +142,7 @@ Update bundled CA certificates from the [Mozilla cURL release][curl]:
 
 Update bundled OpenAPI specification from the canonical repository:
 
-    bundle exec rake update_spec
+    bundle exec rake update_openapi
 
 [api-keys]: https://dashboard.stripe.com/account/apikeys
 [connect]: https://stripe.com/connect

Rakefile

@@ -15,13 +15,13 @@ task :update_certs do
 end
 
 desc "Update OpenAPI specification"
-task :update_spec do
+task :update_openapi do
   require "faraday"
 
   ["fixtures.json", "fixtures.yaml", "spec.json", "spec.yaml"].map { |file|
     Thread.new do
       fetch_file "https://raw.githubusercontent.com/stripe/openapi/master/spec/#{file}",
-        File.expand_path("../spec/#{file}", __FILE__)
+        File.expand_path("../openapi/#{file}", __FILE__)
     end
   }.map { |t| t.join }
 end

test/api_fixtures.rb

@@ -3,7 +3,7 @@
 # tests.
 class APIFixtures
   def initialize
-    @fixtures = ::JSON.parse(File.read("#{PROJECT_ROOT}/spec/fixtures.json"),
+    @fixtures = ::JSON.parse(File.read("#{PROJECT_ROOT}/openapi/fixtures.json"),
       symbolize_names: true)
     freeze_recursively(@fixtures)
   end

test/api_stub_helpers.rb

@@ -95,10 +95,10 @@ module APIStubHelpers
     end
   end
 
-  # Finds the latest OpenAPI specification in ROOT/spec/ and parses it for
+  # Finds the latest OpenAPI specification in ROOT/openapi/ and parses it for
   # use with Committee.
   def self.initialize_spec
-    schema_data = ::JSON.parse(File.read("#{PROJECT_ROOT}/spec/spec.json"))
+    schema_data = ::JSON.parse(File.read("#{PROJECT_ROOT}/openapi/spec.json"))
 
     driver = Committee::Drivers::OpenAPI2.new
     driver.parse(schema_data)