Fixes and suggestions from PR #7 (#8)

* Update README.md

* Update payload.rb

Author: pedrofurtado

README.md

@@ -49,10 +49,14 @@ pix = QrcodePixRuby::Payload.new(
   repeatable:     false
 )
 
+# If needed, change the attributes value later
+pix.pix_key = 'minhaoutrachavepix'
+pix.merchant_city = 'BRASILIA'
+
 # QRCode copia-e-cola
 puts pix.payload
 
-# QRCode para uso em imagens
+# QRCode for images
 puts pix.base64
 ```
 
@@ -70,6 +74,10 @@ pix = QrcodePixRuby::Payload.new(
   repeatable:     false
 )
 
+# If needed, change the attributes value later
+pix.url = 'https://another-example.com'
+pix.amount = 1.50
+
 # QRCode copia-e-cola
 puts pix.payload
 

lib/qrcode_pix_ruby/payload.rb

@@ -71,11 +71,11 @@ def base64
     private
 
     def verify_kwargs(keys)
-      unknows = keys - ATTRIBUTES
+      unknowns = keys - ATTRIBUTES
 
-      return unless unknows.any?
+      return unless unknowns.any?
 
-      raise QrcodePixRuby::PayloadArgumentError, "Unknown attributes: #{unknows.join(', ')}"
+      raise QrcodePixRuby::PayloadArgumentError, "Unknown attributes: #{unknowns.join(', ')}"
     end
 
     def emv(id, value)