submodules: update clippy from 66df92a to c8e3cfb

Changes:
````
travis: temporarily disable rustfmt ci check until rust-lang#4742 is resolved
rustup rust-lang#65792
Fix ICE rust-lang#4579
Add regression test for ICE rust-lang#4579
Run update_lints for Unicode lint
Re-add false positive check
Add raw string regression test for useless_format lint
Re-factor useless_format lint
Update Unicode lint tests
[Backported] Rustup to rust-lang#59545
````

Fixes #rust-lang#65888

Author: matthiaskrgr