Fixes for Python3 version, updated .travis with Python3

Author: Aleffio

.travis.yml

@@ -2,6 +2,7 @@ sudo: true
 language: python
 python:
   - "2.7"
+  - "3.6"
 cache: pip
 install:
   - pip install requests

Adyen/httpclient.py

@@ -1,6 +1,7 @@
 #!/bin/python
 
 from __future__ import absolute_import, division, print_function, unicode_literals
+import sys
 
 try:
     import requests
@@ -23,11 +24,11 @@
     from urllib2 import Request, urlopen, HTTPError
 
 try:
-    # Python 3
-    from io import StringIO
-except ImportError:
     # Python 2
     from StringIO import StringIO
+except ImportError:
+    # Python 3
+    from io import BytesIO
 
 import json as json_lib
 import re
@@ -107,15 +108,23 @@ def handle_header(header_line):
         curl = pycurl.Curl()
         curl.setopt(curl.URL, url)
 
-        stringbuffer = StringIO()
+        if sys.version_info[0] >= 3:
+            stringbuffer = BytesIO()
+        else:
+            stringbuffer = StringIO()
+        #stringbuffer = StringIO()
         curl.setopt(curl.WRITEDATA, stringbuffer)
 
         # Add User-Agent header to request so that the request can be identified as coming
         # from the Adyen Python library.
         headers['User-Agent'] = self.user_agent
 
         # Convert the header dict to formatted array as pycurl needs.
-        header_list = ["%s:%s" % (k,v) for k,v in headers.iteritems()]
+        # header_list = ["%s:%s" % (k,v) for k,v in headers.iteritems()]
+        if sys.version_info[0] >= 3:
+            header_list = ["%s:%s" % (k, v) for k, v in headers.items()]
+        else:
+            header_list = ["%s:%s" % (k, v) for k, v in headers.iteritems()]
         #Ensure proper content-type when adding headers
         if json:
             header_list.append("Content-Type:application/json")
@@ -236,7 +245,7 @@ def _urllib_post(self, url,
         raw_store = json
 
         raw_request = json_lib.dumps(json) if json else urlencode(data)
-        url_request = Request(url,data=raw_request)
+        url_request = Request(url,data=raw_request.encode('utf8'))
         if json:
             url_request.add_header('Content-Type','application/json')
         elif not data:
@@ -251,8 +260,12 @@ def _urllib_post(self, url,
 
         #Adding basic auth is username and password provided.
         if username and password:
-            basicAuthstring = base64.encodestring('%s:%s' % (username,
-                password)).replace('\n', '')
+            if sys.version_info[0] >= 3:
+                basicAuthstring = base64.encodebytes(('%s:%s' % (username,
+                                                                 password)).encode()).decode().replace('\n', '')
+            else:
+                basicAuthstring = base64.encodestring('%s:%s' % (username,
+                                                                 password)).replace('\n', '')
             url_request.add_header("Authorization", "Basic %s" % basicAuthstring)
 
         #Adding the headers to the request.