Fix syntax errors and method calls in code generated by Crystal client generator

Created by: jgaskins

Thank you so much for adding a Crystal client generator! I got a little ambitious and attempted to generate a Stripe API client from their OAS3 definition. From inside that repo, I ran the following:

openapi-generator generate -i openapi/spec3.yaml -g crystal -p shardName=stripe -p moduleName=Stripe -o ../stripe

Then I spun up a new Crystal app:

• crystal init app test_stripe
• Added the generated Crystal shard as a dependency in shard.yml with path: ../stripe
• In my new app's src/test_stripe.cr:

  require "stripe"
  
  Stripe.configure do |c|
    c.api_key = ENV["STRIPE_API_KEY"]
  end
  
  pp Stripe.get_customers

• crystal src/test_stripe.cr

There were a few compiler errors for a Crystal project I spun up to test-drive it and I've gotten all the ones I found nailed down here. For the most part, it just looked like some method calls missed in copying over the Ruby generator. And then there were a couple syntax errors — a stray ] character and unescaped quotes in a string. Nothing major so far.

Unfortunately, I had trouble running the ./mvnw clean package command to check my changes or make sure I've caught everything. I'm getting never-ending exceptions in running it — it looks like the instrumentation to capture the exception is also raising exceptions. So I may need a little guidance there.

/cc @wing328

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