Feature: Support graphql tagged heredoc string literals in non-js files

Thanks for making this awesome plugin. Works great for our js codebase

However our graphql api is written using graphql-ruby and so all of our graphql specs are Ruby files. In these files we define heredoc string literals like this:

```ruby
# spec/whatever_spec.rb

<<~GRAPHQL
query Whatever {
whatever {
id
}
}
GRAPHQL
```

Would it be possible to support Ruby files with this plugin?

If so, is it something a new contributor would be able to tackle? I wouldn't mind taking a stab at implementing it if someone gives me a few pointers where to start.

Thanks again!