The following crates required explicit downgrades:
    arrayvec v0.4.12 -> v0.4.11
    autocfg v0.1.7 -> v0.1.6
    c2-chacha v0.2.3 -> v0.2.2
    ppv-lite86 v0.2.6 -> v0.2.5
    proc-macro2 v1.0.10 -> v1.0.3
error: no matching package named `quote` found
location searched: registry `https://github.com/rust-lang/crates.io-index`
required by package `ff_derive v0.6.0`
    ... which is depended on by `ff v0.6.0`
    ... which is depended on by `bellman v0.6.0`
    ... which is depended on by `librustzcash v0.2.0 (/home/nuttycom/work/zcash)`