idl.d.ts specifies the wrong type for IDL.encode

[bdemann]

It specifies that the return type is an ArrayBuffer but it is actually a Uint8Array. Until such a time as @dfinity/candid is updated to reflect the correct types any time that we want to get an ArrayBuffer from IDL.encode we have to get the buffer property from the result. This causes out typechecking to break since ArrayBuffer doesn't have a buffer property. As a result in all the places where this happens (Though I can only think of one in the reply API) we need to ignore the error

dfinity/agent-js#950