Fix two typos in hpack.py

Author: foolip

hpack/hpack.py

@@ -132,7 +132,7 @@ def decode_integer(data, prefix_bits):
 def _dict_to_iterable(header_dict):
     """
     This converts a dictionary to an iterable of two-tuples. This is a
-    HPACK-specific function becuase it pulls "special-headers" out first and
+    HPACK-specific function because it pulls "special-headers" out first and
     then emits them.
     """
     assert isinstance(header_dict, dict)
@@ -387,7 +387,7 @@ class Decoder(object):
         If this amount of data is exceeded, a `OversizedHeaderListError
         <hpack.OversizedHeaderListError>` exception will be raised. At this
         point the connection should be shut down, as the HPACK state will no
-        longer be useable.
+        longer be usable.
 
         Defaults to 64kB.
     :type max_header_list_size: ``int``