Bind Puma socket in container

According to this [blog post][blag], Puma is not happy with the
socket being in a mounted volume. Not sure how this ever worked, but
this fixed it.

[blag]: https://qiita-com.translate.goog/naomichi-y/items/1e676139e3f9fbc75d3c?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp#%E3%82%BD%E3%82%B1%E3%83%83%E3%83%88%E9%80%9A%E4%BF%A1%E3%82%92%E8%A1%8C%E3%81%86%E3%82%A2%E3%83%97%E3%83%AA%E3%82%B1%E3%83%BC%E3%82%B7%E3%83%A7%E3%83%B3%E3%81%8C%E8%B5%B7%E5%8B%95%E3%81%97%E3%81%AA%E3%81%84

ruby/sinatra-puma/app/config/puma.rb

@@ -15,7 +15,7 @@
 environment "production"
 
 # Set up socket location
-bind "unix:///#{shared_dir}/sockets/puma.sock"
+bind "unix:///var/run/puma.sock"
 
 # stdout_redirect "#{shared_dir}/log/puma.stdout.log", "#{shared_dir}/log/puma.stderr.log", true