use six library for isinstance (#66)

Author: ashtul

redisearch/_util.py

@@ -3,7 +3,7 @@
 def to_string(s):
     if isinstance(s, six.string_types):
         return s
-    elif isinstance(s, bytes):
+    elif isinstance(s, six.binary_type):
         return s.decode('utf-8')
     else:
         return s  # Not a string we care about

redisearch/client.py

@@ -499,7 +499,7 @@ def spellcheck(self, query, distance=None, include=None, exclude=None):
             return corrections
 
         for _correction in raw:
-            if isinstance(_correction, long) and _correction == 0:
+            if isinstance(_correction, six.integer_types) and _correction == 0:
                 continue
 
             if len(_correction) != 3: