Ensure a `sha256` or `generateHash` function is provided
Ensure a `sha256` or `generateHash` function is provided

We're no longer providing a SHA-256 function by default, so these
changes ensure that an appropriate function is provided by
developers. Developers can choose to supply a SHA-256 function
via the `sha256` option, if they want the default hash generation
capabilities of the Link (e.g. sha256(print(query))), or they
can override the hashing process completely by supplying a
custom `generateHash` function.

apollographql/apollo-client,apollographql/apollo-client