fix saving request: binary flag is needed on windows

lib/paymentrequest.py

@@ -110,7 +110,7 @@ class PaymentRequest:
 
         self.id = bitcoin.sha256(r)[0:16].encode('hex')
         filename = os.path.join(self.dir_path, self.id)
-        with open(filename,'w') as f:
+        with open(filename,'wb') as f:
             f.write(r)
 
         return self.parse(r)
@@ -125,7 +125,7 @@ class PaymentRequest:
 
     def read_file(self, key):
         filename = os.path.join(self.dir_path, key)
-        with open(filename,'r') as f:
+        with open(filename,'rb') as f:
             r = f.read()
 
         assert key == bitcoin.sha256(r)[0:16].encode('hex')