title: warning: constant ::Fixnum is deprecated When generating new model
body: <p>I've tried to find some solution for this, but I really couldn't find anything related with the errors that is appearing to me when I run the rails command: </p>
  
  <blockquote>
    <p>rails generate model Book title:string summary:text isbn:string</p>
  </blockquote>
  
  <pre><code>/home/vmu/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.0.1/lib/active_support/xml_mini.rb:51: warning: constant ::Fixnum is deprecated
  /home/vmu/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.0.1/lib/active_support/xml_mini.rb:52: warning: constant ::Bignum is deprecated
  /home/vmu/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.0.1/lib/active_support/core_ext/numeric/conversions.rb:138: warning: constant ::Fixnum is deprecated
  Running via Spring preloader in process 3579
  Expected string default value for '--jbuilder'; got true (boolean)
        invoke  active_record
     identical    db/migrate/20170104114702_create_books.rb
     identical    app/models/book.rb
        invoke    test_unit
     identical      test/models/book_test.rb
     identical      test/fixtures/books.yml
  </code></pre>
  
  <p>Anyone know what may be causing these errors?</p>