Don't hardcode libknot.so version number.

Index: libknot/__init__.py
--- libknot/__init__.py.orig
+++ libknot/__init__.py
@@ -46,7 +46,7 @@ class Knot(object):
             if sys.platform == "darwin":
                 path = "libknot%s.dylib" % version
             else:
-                path = "libknot.so%s" % version
+                path = "libknot.so"
 
         cls.LIBKNOT = ctypes.cdll.LoadLibrary(path)