Failing builds with clippy errors against latest stable rust version.

[tublitzed]

Ie, here

error: match expression looks like `matches!` macro
  --> src/db/tests/batch.rs:90:34
   |
90 |           ApiErrorKind::Db(dbe) => match dbe.kind() {
   |  __________________________________^
91 | |             DbErrorKind::BatchNotFound => true,
92 | |             _ => false,
93 | |         },
   | |_________^ help: try this: `matches!(dbe.kind(), DbErrorKind::BatchNotFound)`
   |
   = note: `-D clippy::match-like-matches-macro` implied by `-D warnings`
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#match_like_matches_macro

error: match expression looks like `matches!` macro
   --> src/db/transaction.rs:224:27
    |
224 |               let is_read = match method {
    |  ___________________________^
225 | |                 Method::GET | Method::HEAD => true,
226 | |                 _ => false,
227 | |             };
    | |_____________^ help: try this: `matches!(method, Method::GET | Method::HEAD)`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#match_like_matches_macro

error: aborting due to 2 previous errors

I'm wondering if it's worth changing our circle config from defaulting to rust stable to instead defaulting to the version of rust that we're using in the app?