Add support for generating then gem on a windows platform

Description

Currently the template for generating the swagger_client_gemspec assums that it is executing in a linuz based platform and utilized the find command to gather all necessary files to include in the gem file. This fails if executing in a windows platform.

Swagger-codegen version

Swagger Codegen 3.0.0

Swagger declaration file content or url

# -*- encoding: utf-8 -*-

=begin
{{> api_info}}
=end

$:.push File.expand_path("../lib", __FILE__)
require "{{gemName}}/version"

Gem::Specification.new do |s|
  s.name        = "{{gemName}}{{^gemName}}{{{appName}}}{{/gemName}}"
  s.version     = {{moduleName}}::VERSION
  s.platform    = Gem::Platform::RUBY
  s.authors     = ["{{gemAuthor}}{{^gemAuthor}}Swagger-Codegen{{/gemAuthor}}"]
  s.email       = ["{{gemAuthorEmail}}{{^gemAuthorEmail}}{{infoEmail}}{{/gemAuthorEmail}}"]
  s.homepage    = "{{gemHomepage}}{{^gemHomepage}}https://github.com/swagger-api/swagger-codegen{{/gemHomepage}}"
  s.summary     = "{{gemSummary}}{{^gemSummary}}{{{appName}}} Ruby Gem{{/gemSummary}}"
  s.description = "{{gemDescription}}{{^gemDescription}}{{{appDescription}}}{{^appDescription}}{{{appName}}} Ruby Gem{{/appDescription}}{{/gemDescription}}"
  {{#gemLicense}}
  s.license     = '{{{gemLicense}}}'
  {{/gemLicense}}
  {{^gemLicense}}
  s.license     = "Unlicense"
  {{/gemLicense}}
  s.required_ruby_version = "{{{gemRequiredRubyVersion}}}{{^gemRequiredRubyVersion}}>= 1.9{{/gemRequiredRubyVersion}}"

  s.add_runtime_dependency 'typhoeus', '~> 1.0', '>= 1.0.1'
  s.add_runtime_dependency 'json', '~> 2.1', '>= 2.1.0'

  s.add_development_dependency 'rspec', '~> 3.6', '>= 3.6.0'

  s.files         = `find *`.split("\n").uniq.sort.select { |f| !f.empty? }
  s.test_files    = `find spec/*`.split("\n")
  s.files = Dir.glob('lib/**/*') + %w{Rakefile README.md}  
  s.executables   = []
  s.require_paths = ["lib"]
end

Suggest a fix/enhancement

# -*- encoding: utf-8 -*-

=begin
{{> api_info}}
=end

$:.push File.expand_path("../lib", __FILE__)
require "{{gemName}}/version"

Gem::Specification.new do |s|
  s.name        = "{{gemName}}{{^gemName}}{{{appName}}}{{/gemName}}"
  s.version     = {{moduleName}}::VERSION
  s.platform    = Gem::Platform::RUBY
  s.authors     = ["{{gemAuthor}}{{^gemAuthor}}Swagger-Codegen{{/gemAuthor}}"]
  s.email       = ["{{gemAuthorEmail}}{{^gemAuthorEmail}}{{infoEmail}}{{/gemAuthorEmail}}"]
  s.homepage    = "{{gemHomepage}}{{^gemHomepage}}https://github.com/swagger-api/swagger-codegen{{/gemHomepage}}"
  s.summary     = "{{gemSummary}}{{^gemSummary}}{{{appName}}} Ruby Gem{{/gemSummary}}"
  s.description = "{{gemDescription}}{{^gemDescription}}{{{appDescription}}}{{^appDescription}}{{{appName}}} Ruby Gem{{/appDescription}}{{/gemDescription}}"
  {{#gemLicense}}
  s.license     = '{{{gemLicense}}}'
  {{/gemLicense}}
  {{^gemLicense}}
  s.license     = "Unlicense"
  {{/gemLicense}}
  s.required_ruby_version = "{{{gemRequiredRubyVersion}}}{{^gemRequiredRubyVersion}}>= 1.9{{/gemRequiredRubyVersion}}"

  s.add_runtime_dependency 'typhoeus', '~> 1.0', '>= 1.0.1'
  s.add_runtime_dependency 'json', '~> 2.1', '>= 2.1.0'

  s.add_development_dependency 'rspec', '~> 3.6', '>= 3.6.0'
  s.files = Dir.glob('lib/**/*') + %w{Rakefile README.md}  
  s.executables   = []
  s.require_paths = ["lib"]
end

Search the generator templates for the shown swagger_client_gemspec content and inspect how generated Ruby gemspec files are assembled. Replace the platform-dependent file discovery behavior with a cross-platform approach, then verify that generated gemspecs include the intended files on Windows as well as Unix-like systems.