在linux vps上，运行cargo build --release遇错

[luckypoem]

hi.

[root@bwg-vps bit-tunnel-by-bit-ranger]# cargo build --release
Updating crates.io index
Fetch [==========================================> ] 79.79%
Downloaded rand v0.7.3
Downloaded getopts v0.2.21
Downloaded futures-timer v1.0.3
Downloaded async-std v1.5.0
Downloaded rust-crypto v0.2.36
Downloaded getrandom v0.1.14
Downloaded libc v0.2.68
Downloaded num_cpus v1.12.0
Downloaded pin-project-lite v0.1.4
Downloaded async-task v1.3.1
Downloaded futures-io v0.3.4
Downloaded futures-core v0.3.4
Downloaded crossbeam-deque v0.7.3
Downloaded rand_chacha v0.2.2
Downloaded crossbeam-utils v0.7.2
Downloaded memchr v2.3.3
Downloaded kv-log-macro v1.0.4
Downloaded futures-timer v2.0.2
Downloaded once_cell v1.3.1
Downloaded crossbeam-channel v0.4.2
Downloaded broadcaster v1.0.0
Downloaded rustc-serialize v0.3.24
Downloaded crossbeam-epoch v0.8.2
Downloaded futures-util v0.3.4
Downloaded gcc v0.3.55
Downloaded futures-channel v0.3.4
Downloaded autocfg v1.0.0
Downloaded parking_lot v0.10.0
Downloaded futures-sink v0.3.4
Downloaded futures-macro v0.3.4
Downloaded scopeguard v1.1.0
Downloaded proc-macro-hack v0.5.14
Downloaded proc-macro-nested v0.1.4
Downloaded memoffset v0.5.4
Downloaded futures-task v0.3.4
Downloaded proc-macro2 v1.0.9
Downloaded syn v1.0.17
Downloaded parking_lot_core v0.7.0
Downloaded lock_api v0.3.3
Downloaded quote v1.0.3
Downloaded smallvec v1.2.0
Compiling libc v0.2.68
Compiling cfg-if v0.1.10
Compiling autocfg v1.0.0
Compiling proc-macro2 v1.0.9
Compiling unicode-xid v0.2.0
Compiling maybe-uninit v2.0.0
Compiling scopeguard v1.1.0
Compiling syn v1.0.17
Compiling log v0.4.8
Compiling proc-macro-nested v0.1.4
Compiling getrandom v0.1.14
Compiling lazy_static v1.4.0
Compiling slab v0.4.2
Compiling futures-sink v0.3.4
Compiling smallvec v1.2.0
Compiling pin-utils v0.1.0-alpha.4
Compiling proc-macro-hack v0.5.14
Compiling futures-core v0.3.4
Compiling gcc v0.3.55
Compiling futures-task v0.3.4
Compiling memchr v2.3.3
Compiling ppv-lite86 v0.2.6
Compiling once_cell v1.3.1
Compiling futures-core-preview v0.3.0-alpha.19
Compiling futures-io v0.3.4
Compiling futures-timer v2.0.2
Compiling pin-project-lite v0.1.4
Compiling rustc-serialize v0.3.24
Compiling unicode-width v0.1.7
Compiling crossbeam-utils v0.7.2
Compiling memoffset v0.5.4
Compiling crossbeam-epoch v0.8.2
Compiling lock_api v0.3.3
Compiling futures-channel v0.3.4
Compiling futures-timer v1.0.3
Compiling rust-crypto v0.2.36
Compiling getopts v0.2.21
error[E0658]: cfg(doctest) is experimental and subject to change
--> /root/.cargo/registry/src/github.com-1ecc6299db9ec823/memoffset-0.5.4/src/lib.rs:72:7
|
72 | #[cfg(doctest)]
| ^^^^^^^
|
= note: for more information, see rust-lang/rust#62210
= help: add #![feature(cfg_doctest)] to the crate attributes to enable

error[E0658]: cfg(doctest) is experimental and subject to change
--> /root/.cargo/registry/src/github.com-1ecc6299db9ec823/memoffset-0.5.4/src/lib.rs:75:7
|
75 | #[cfg(doctest)]
| ^^^^^^^
|
= note: for more information, see rust-lang/rust#62210
= help: add #![feature(cfg_doctest)] to the crate attributes to enable

error: aborting due to 2 previous errors

For more information about this error, try rustc --explain E0658.
error: could not compile memoffset.
warning: build failed, waiting for other jobs to finish...
error: build failed
[root@bwg-vps bit-tunnel-by-bit-ranger]#

怎么解决？

[bit-ranger]

rust版本过低？我的版本是:
ubuntu 18.04.3 LTS
rustc 1.42.0

[luckypoem]

嗯，我vps上的rust版本有点低，为1.40. 运行rustup update ，升级为最新版，然后运行cargo build --release就ok.