Improve error messages on bin/setup

`system(.., exception: true)` gives you more information on how the
command failed, e.g.

```
bin/setup:8:in `system': Command failed with exit 1: bundle install (RuntimeError)

bin/setup:8:in `system': No such file or directory - bundle (Errno::ENOENT)
```

Author: k0kubun

railties/lib/rails/generators/rails/app/templates/bin/setup.tt

@@ -4,7 +4,7 @@ require "fileutils"
 APP_ROOT = File.expand_path("..", __dir__)
 
 def system!(*args)
-  system(*args) || abort("\n== Command #{args} failed ==")
+  system(*args, exception: true)
 end
 
 FileUtils.chdir APP_ROOT do