Rephrase error message.

Author: anhu

wolfssl/_methods.py

@@ -108,7 +108,7 @@ def __init__(self, protocol, server_side):
                 _lib.wolfDTLSv1_3_client_method()
 
         if self.native_object == _ffi.NULL:
-            raise MemoryError("Unnable to allocate method object")
+            raise MemoryError("Cannot allocate method object")
 
     def __del__(self):
         if getattr(self, 'native_object', _ffi.NULL) != _ffi.NULL: