Map node binaries whenever rvm1:hook is called and evaluate the fnm_setup_command dynamically

The previous version worked fine when using Capistrano to deploy a new
release, but it did not work for other commands, like `cap npm install`
or `cap puma:start`, as they do not create a release. Therefore, the
`git:create_release` was never called, and the `map_node_bins` was not
invoked.

Since we need node binaries available to the deploy user when executing
any process that runs the application, like puma, delayed_job, and rake
tasks, among others, it makes sense to load FNM to use the correct Node
version in the same places where Capistrano loads RVM to load the correct
Ruby version.

With dynamic loading of the `fnm_setup_command`, we get the correct path
when deploying a new release and also when running any other capistrano
command that does not deploy a new release.

config/deploy.rb

@@ -60,7 +60,7 @@ namespace :deploy do
   Rake::Task["delayed_job:default"].clear_actions
   Rake::Task["puma:smart_restart"].clear_actions
 
-  after "git:create_release", "map_node_bins"
+  after "rvm1:hook", "map_node_bins"
 
   after :updating, "install_node"
   after :updating, "install_ruby"
@@ -127,7 +127,7 @@ task :map_node_bins do
   on roles(:app) do
     within release_path do
       with rails_env: fetch(:rails_env) do
-        prefix = "#{fetch(:fnm_setup_command)} && fnm exec"
+        prefix = -> { "#{fetch(:fnm_setup_command)} && fnm exec" }
 
         fetch(:fnm_map_bins).each do |command|
           SSHKit.config.command_map.prefix[command.to_sym].unshift(prefix)