0.8.11 Compilation Error

[uranuspool]

Describe the bug
A clear and concise description of what the bug is.

Mandatory Information

1. Current version 0.8.9, trying to update to 0.8.11:

jcli 0.8.9 (heads/v0.8.9-30d20d2e, release, linux [x86_64]) - [rustc 1.38.0 (625451e37 2019-09-23)]
2. Current version 0.8.9, trying to update to 0.8.11:

jormungandr 0.8.9 (heads/v0.8.9-30d20d2e, release, linux [x86_64]) - [rustc 1.41.0 (5e1a79984 2020-01-27)]

To Reproduce
Steps to reproduce the behavior:

1. Clone jormungandr
2. Start compilation:

cargo install --path jormungandr --force

3. During compilation the following error occurs:

Compiling syn v1.0.14
Compiling libc v0.2.66
Compiling log v0.4.8
Compiling proc-macro-nested v0.1.3
Compiling futures-sink v0.3.4
Compiling futures-core v0.3.4
Compiling futures-io v0.3.4
Compiling futures-task v0.3.4
Compiling pin-utils v0.1.0-alpha.4
Compiling arc-swap v0.4.4
Compiling untrusted v0.7.0
Compiling bytes v0.5.4
Compiling pin-project-lite v0.1.4
Compiling spin v0.5.2
Compiling copyless v0.1.4
Compiling fixedbitset v0.1.9
Compiling remove_dir_all v0.5.2
Compiling multimap v0.4.0
Compiling base64 v0.11.0
Compiling sha1 v0.6.0
Compiling language-tags v0.2.2
Compiling slog v2.5.2

error: core::slice::<impl [T]>::len is not yet stable as a const fn
--> /root/.cargo/registry/src/jackfan.us.kg-1ecc6299db9ec823/bytes-0.5.4/src/bytes.rs:130:18
|
130 | len: bytes.len(),
| ^^^^^^^^^^^

Compiling tower-service v0.3.0
error: aborting due to previous error

error: Could not compile bytes.
warning: build failed, waiting for other jobs to finish...
error: failed to compile jormungandr v0.8.11 (/srv/jormungandr/jormungandr), intermediate artifacts can be found at /srv/jormungandr/target

Caused by:
build failed

Similar behavior occurs when compiling jcli:

# cargo install --path jcli --force
Installing jcli v0.8.11 (/srv/jormungandr/jcli)
Updating crates.io index
Compiling structopt v0.2.18
Compiling chain-impl-mockchain v0.1.0 (/srv/jormungandr/chain-deps/chain-impl-mockchain)
Compiling hyper-tls v0.3.2
Compiling reqwest v0.9.24
error[E0658]: use of unstable library feature 'weak_counts'
--> chain-deps/chain-impl-mockchain/src/multiverse.rs:85:48
|
85 | GcEntry::Collectable(weak) => weak.strong_count() == 0,
| ^^^^^^^^^^^^
|
= note: for more information, see rust-lang/rust#57977

error: aborting due to previous error

For more information about this error, try rustc --explain E0658.
error: Could not compile chain-impl-mockchain.
warning: build failed, waiting for other jobs to finish...
error: failed to compile jcli v0.8.11 (/srv/jormungandr/jcli), intermediate artifacts can be found at /srv/jormungandr/target

Caused by:
build failed

Expected behavior
Both jormungandr and jcli should compile without any problems.

[vincenthz]

your stable rust compiler is too old, update to 1.41