Not possible to set headers on a SendEmailRequest

[Mange]

The SendEmailRequest class accepts a headers: option, but the value provided will always be overwritten with an empty hash. See line 10 below:

customerio-ruby/lib/customerio/requests/send_email_request.rb

Lines 7 to 11 in 5f310b8

	def initialize(opts)
	@message = opts.delete_if { |field| invalid_field?(field) }
	@message[:attachments] = {}
	@message[:headers] = {}
	end

Is this a typo for ||=?

For now I'll work around it by modifying the returned object directly.