Fix working dir bug when composer:run is executed directly via the CLI

When not running via a deploy (e.g. composer:run executed directly via CLI), the command fails because
the release_path variable is not set. It's only set as part of a deploy.

This fix changes the way composer:run works: when not executed within the context of a deploy, Composer's
working directory will be set to current_path instead of release_path.

This is a backwards-compatible bugfix, but it might be worth bumping at least minor version because
behavior changes considerably for end-users.

lib/capistrano/tasks/composer.rake

@@ -28,7 +28,14 @@ namespace :composer do
   task :run, :command do |t, args|
     args.with_defaults(:command => :list)
     on release_roles(fetch(:composer_roles)) do
-      within fetch(:composer_working_dir) do
+
+      composer_working_dir = fetch(:composer_working_dir)
+      if composer_working_dir.nil? # not in deploy context? (e.g. task was executed directly)
+        # run in current_path
+        composer_working_dir = current_path
+      end
+
+      within composer_working_dir do
         execute :composer, args[:command], *args.extras
       end
     end