Tweak to dates for RFCs in bibliography.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

protocol/zcash.bib

@@ -139,7 +139,8 @@ Lecture Notes in Computer Science; Springer, 2013.},
    author={Markku-Juhani Saarinen (ed.)},
    title={Request for {C}omments 7693: {T}he {BLAKE2} {C}ryptographic {H}ash and
 {M}essage {A}uthentication {C}ode ({MAC})},
-   howpublished={Internet Engineering Task Force (IETF). November 2015},
+   howpublished={Internet Engineering Task Force (IETF)},
+   date={2015-11},
    url={https://tools.ietf.org/html/rfc7693},
    urldate={2016-08-31}
 }
@@ -294,6 +295,7 @@ Received \mbox{April 13,} 2011.}
    author={Yoav Nir and Adam Langley},
    title={Request for {C}omments 7539: Cha{C}ha20 and {P}oly1305 for {IETF} {P}rotocols},
    howpublished={Internet Research Task Force (IRTF)},
+   date={2015-05},
    url={https://tools.ietf.org/html/rfc7539},
    urldate={2016-09-02},
    addendum={As modified by verified errata at \url{https://www.rfc-editor.org/errata_search.php?rfc=7539}