docs: fix simple typo, specifed -> specified

There is a small typo in src/snappy/snappy_formats.py.

Should read `specified` rather than `specifed`.

Author: timgates42

src/snappy/snappy_formats.py

@@ -3,7 +3,7 @@
 get_decompress_function - returns stream decompress function for a current
     format (specified or autodetected)
 get_compress_function - returns compress function for a current format
-    (specifed or default)
+    (specified or default)
 """
 from __future__ import absolute_import