Downgrade Sinatra for Padrino tests
Downgrade Sinatra for Padrino tests

Sinatra 3 has just been released but doesn't work nice with Padrino yet
I think.

It raises a FrozenError about a frozen array that cannot be modified.
We're not creating Padrino apps in a weird way, other than them being
anonymous classes. If I used a standard class, e.g. `class MyApp <
Padrino::Application`, like the docs say, it doesn't fix it.

```
FrozenError: can't modify frozen Array: [
  /\/sinatra(\/(base|main|show_exceptions))?\.rb$/,
  /lib\/tilt.*\.rb$/,
  /^\(.*\)$/,
  /rubygems\/(custom|core_ext\/kernel)_require\.rb$/,
  /active_support/,
  /bundler(\/(?:runtime|inline))?\.rb/,
  /<internal:/
]
```

Downgrade Sinatra in the Padrino tests until it's resolved in Padrino.
I don't think this is an issue on our end.

[skip changeset]

appsignal/appsignal-ruby,appsignal/appsignal-ruby,appsignal/appsignal-ruby,appsignal/appsignal-ruby