Sinatra Spy does not set endpoint name if Error inside endpoint

## Describe the bug

Transaction name is "Rack" (because of Rack Middleware) if an error happens inside the endpoint.

## Steps to reproduce
Create Sinatra application, throw an error inside the endpoint like:

```
def hello
raise MyError
end
```

## Expected behavior

Sinatra Spy should update transaction name even if Error occurs

Current code:

```
class SinatraSpy
# @api private
module Ext
def dispatch!(*args, &block)
super(*args, &block).tap do # <------- Error occurs inside here! (sometimes)
next unless (transaction = ElasticAPM.current_transaction)
next unless (route = env['sinatra.route'])

transaction.name = route # <----------- this should get called regardless!
end
end
```

My suggestion:

```
class SinatraSpy
# @api private
module Ext
def dispatch!(*args, &block)
begin
super(*args, &block)
ensure
if (transaction = ElasticAPM.current_transaction) && (route = env['sinatra.route'])
transaction.name = route
end
end
end
```