Update the license to VNPL 1.1

VNPL 1.1 is slightly reworded to make it clear that proprietary software
interacting with Vitastor and providing some kind of service to end users isn't
a "Proxy Program" if it's not specially designed to be used with Vitastor.

For example, Windows OS running in a virtual machine stored in a Vitastor
cluster clearly isn't.

allocator.cpp

@@ -1,5 +1,5 @@
 // Copyright (c) Vitaliy Filippov, 2019+
-// License: VNPL-1.0 (see README.md for details)
+// License: VNPL-1.1 (see README.md for details)
 
 #include <stdexcept>
 #include "allocator.h"