Update README script for Python 3.6

Author: thinkingserious

register.py

@@ -3,12 +3,12 @@
 
 output = pypandoc.convert('README.md', 'rst')
 f = open('README.txt','w+')
-f.write(output.encode('utf-8'))
+f.write(str(output.encode('utf-8')))
 f.close()
 
 readme_rst = open('./README.txt').read()
 replace = '.. figure:: https://uiux.s3.amazonaws.com/2016-logos/email-logo%402x.png\n   :alt: SendGrid Logo\n\n   SendGrid Logo\n'
 replacement = '|SendGrid Logo|\n\n.. |SendGrid Logo| image:: https://uiux.s3.amazonaws.com/2016-logos/email-logo%402x.png\n   :target: https://www.sendgrid.com'
 final_text = readme_rst.replace(replace,replacement)
 with open('./README.txt', 'w') as f:
-  f.write(final_text.encode('utf-8'))
+  f.write(final_text)