class Restforce::Middleware::RaiseError

def call(env)

an implementation of `#call` by default
Required for Faraday versions pre-v1.2.0 which do not include 
def call(env)
  on_request(env) if respond_to?(:on_request)
  @app.call(env).on_complete do |environment|
    on_complete(environment) if respond_to?(:on_complete)
  end
end