Use only snake cased symbols in commands.

Mixing strings and symbols seems aesthetically less than ideal.

We can also use underscores just fine. Thor converts them to dashes
for the CLI and it makes access in Ruby code nicer.

Here's the `server --help` output after this change:

```
Usage:
  rails server [thin/puma/webrick] [options]

Options:
  -p, [--port=port]                        # Runs Rails on the specified port - defaults to 3000.
  -b, [--binding=IP]                       # Binds Rails to the specified IP - defaults to 'localhost' in development and '0.0.0.0' in other environments'.
  -c, [--config=file]                      # Uses a custom rackup configuration.
                                           # Default: config.ru
  -d, [--daemon], [--no-daemon]            # Runs server as a Daemon.
  -e, [--environment=name]                 # Specifies the environment to run this server under (development/test/production).
  -u, [--using=name]                       # Specifies the Rack server used to run the application (thin/puma/webrick).
  -P, [--pid=PID]                          # Specifies the PID file.
                                           # Default: tmp/pids/server.pid
  -C, [--dev-caching], [--no-dev-caching]  # Specifies whether to perform caching in development.
      [--early-hints], [--no-early-hints]  # Enables HTTP/2 early hints.
```

See? Quite dashing ✨

1 files changed, 5 insertions, 5 deletions

diff --git a/railties/lib/rails/commands/server/server_command.rb b/railties/lib/rails/commands/server/server_command.rb
index cf17f0ef12..4fcb10d53f 100644
--- a/railties/lib/rails/commands/server/server_command.rb
+++ b/railties/lib/rails/commands/server/server_command.rb
@@ -132,10 +132,10 @@ module Rails
         desc: "Specifies the Rack server used to run the application (thin/puma/webrick).", banner: :name
       class_option :pid, aliases: "-P", type: :string, default: DEFAULT_PID_PATH,
         desc: "Specifies the PID file."
-      class_option "dev-caching", aliases: "-C", type: :boolean, default: nil,
+      class_option :dev_caching, aliases: "-C", type: :boolean, default: nil,
         desc: "Specifies whether to perform caching in development."
-      class_option "restart", type: :boolean, default: nil, hide: true
-      class_option "early_hints", type: :boolean, default: nil, desc: "Enables HTTP/2 early hints."
+      class_option :restart, type: :boolean, default: nil, hide: true
+      class_option :early_hints, type: :boolean, default: nil, desc: "Enables HTTP/2 early hints."
 
       def initialize(args = [], local_options = {}, config = {})
         @original_options = local_options
@@ -177,7 +177,7 @@ module Rails
             environment:           environment,
             daemonize:             options[:daemon],
             pid:                   pid,
-            caching:               options["dev-caching"],
+            caching:               options[:dev_caching],
             restart_cmd:           restart_command,
             early_hints:           early_hints
           }
@@ -210,7 +210,7 @@ module Rails
                   name = :Port
                 when :binding
                   name = :Host
-                when :"dev-caching"
+                when :dev_caching
                   name = :caching
                 when :daemonize
                   name = :daemon