A proposal is revoked—
    (1) by the communication of notice of revocation by the proposer to the other party;
    (2) by the lapse of the time prescribed in such proposal for its acceptance, or, if no time is so prescribed, by the lapse of a reasonable time, without communication of the acceptance;
    (3) by the failure of the acceptor to fulfil a condition precedent to acceptance; or
    (4) by the death or insanity of the proposer, if the fact of his death or insanity comes to the knowledge of the acceptor before acceptance.