Running `cf push` with this app generates a lot of deprecation warnings

[willmurphyscode]

I recently cloned this repo and ran cf push pointed to a recent Cloud Foundry instance. A lot of deprecation warnings were printed when I did this, mostly during Rails asset precompilation. This might not be the most polished first experience of CF if people are using it in training or using it to learn.

To repro:

$ git clone https://github.com/cloudfoundry-samples/cf-sample-app-rails
$ cd cf-sample-app-rails
$ cf push cf-rails-sample

Sample of warnings:

   /tmp/contents755917043/deps/0/vendor_bundle/ruby/2.5.0/gems/activesupport-5.0.1/lib/active_support/xml_mini.rb:51: warning: constant ::Fixnum is deprecated
   /tmp/contents755917043/deps/0/vendor_bundle/ruby/2.5.0/gems/activesupport-5.0.1/lib/active_support/xml_mini.rb:52: warning: constant ::Bignum is deprecated
   -----> Saving vendor_bundle to cache
   -----> Finalizing Ruby
   -----> Precompiling assets
          /tmp/contents755917043/deps/0/vendor_bundle/ruby/2.5.0/gems/activesupport-5.0.1/lib/active_support/xml_mini.rb:51: warning: constant ::Fixnum is deprecated
          /tmp/contents755917043/deps/0/vendor_bundle/ruby/2.5.0/gems/activesupport-5.0.1/lib/active_support/xml_mini.rb:52: warning: constant ::Bignum is deprecated
          DEPRECATION WARNING: `config.serve_static_files` is deprecated and will be removed in Rails 5.1.
          Please use `config.public_file_server.enabled = false` instead.
           (called from block in <top (required)> at /tmp/app/config/environments/production.rb:25)
          /tmp/contents755917043/deps/0/vendor_bundle/ruby/2.5.0/gems/activesupport-5.0.1/lib/active_support/core_ext/numeric/conversions.rb:138: warning: constant ::Fixnum is deprecated
          I, [2019-05-17T16:59:04.525041 #1343]  INFO -- : Writing /tmp/app/public/assets/cloud-foundry-31071fc0c7d3275efbc76242836ee1a96a3a10081b9e41f4c7c1b6a6f482048b.svg
          I, [2019-05-17T16:59:04.526234 #1343]  INFO -- : Writing /tmp/app/public/assets/cloud-foundry-31071fc0c7d3275efbc76242836ee1a96a3a10081b9e41f4c7c1b6a6f482048b.svg.gz
          I, [2019-05-17T16:59:04.531239 #1343]  INFO -- : Writing /tmp/app/public/assets/ruby_logo-a91a3ee3b3ac1e0ba95e964651b09e1124633a893a8e7e8f2f47dd57196e7bfb.svg
          I, [2019-05-17T16:59:04.532122 #1343]  INFO -- : Writing /tmp/app/public/assets/ruby_logo-a91a3ee3b3ac1e0ba95e964651b09e1124633a893a8e7e8f2f47dd57196e7bfb.svg.gz
          I, [2019-05-17T16:59:04.687263 #1343]  INFO -- : Writing /tmp/app/public/assets/the-rabbit-d69e3bb5d732865c27d1f09ded347a5fb7ccfcca6ffa71991bec12e2898e78eb.svg
          I, [2019-05-17T16:59:04.689155 #1343]  INFO -- : Writing /tmp/app/public/assets/the-rabbit-d69e3bb5d732865c27d1f09ded347a5fb7ccfcca6ffa71991bec12e2898e78eb.svg.gz
          I, [2019-05-17T16:59:12.002128 #1343]  INFO -- : Writing /tmp/app/public/assets/application-b881d5e85b8424bf1248c100dc67bfe7f39131307bfc94f9e5ee1edac3ce5011.js
          I, [2019-05-17T16:59:12.004036 #1343]  INFO -- : Writing /tmp/app/public/assets/application-b881d5e85b8424bf1248c100dc67bfe7f39131307bfc94f9e5ee1edac3ce5011.js.gz
          I, [2019-05-17T16:59:12.024148 #1343]  INFO -- : Writing /tmp/app/public/assets/application-e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855.css
          I, [2019-05-17T16:59:12.024416 #1343]  INFO -- : Writing /tmp/app/public/assets/application-e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855.css.gz
          Asset precompilation completed (10.176594154s)
          Cleaning assets
          /tmp/contents755917043/deps/0/vendor_bundle/ruby/2.5.0/gems/activesupport-5.0.1/lib/active_support/xml_mini.rb:51: warning: constant ::Fixnum is deprecated
          /tmp/contents755917043/deps/0/vendor_bundle/ruby/2.5.0/gems/activesupport-5.0.1/lib/active_support/xml_mini.rb:52: warning: constant ::Bignum is deprecated
          DEPRECATION WARNING: `config.serve_static_files` is deprecated and will be removed in Rails 5.1.
          Please use `config.public_file_server.enabled = false` instead.
           (called from block in <top (required)> at /tmp/app/config/environments/production.rb:25)
          /tmp/contents755917043/deps/0/vendor_bundle/ruby/2.5.0/gems/activesupport-5.0.1/lib/active_support/core_ext/numeric/conversions.rb:138: warning: constant ::Fixnum is deprecated