submodules: update clippy from 754b4c0 to b2601be

Changes:
````
Fix NAIVE_BYTECOUNT applicability
Fix dogfood error
Change Applicability of MISTYPED_LITERAL_SUFFIX
Add applicability level to (nearly) every span_lint_and_sugg function
Update stderr file
Fix bugs and improve documentation
Add Applicability::Unspecified to span_lint_and_sugg functions
Introduce snippet_with_applicability and hir_with_applicability functions
readme: tell how to install clippy on travis from git if it is not shipped with a nightly.
constants: add u128 i128 builtin types and fix outdated url
Update lints
Lint only the first statment/expression after alloc
Fix some warnings related to Self
Rename some symbols
Split lint into slow and unsafe vector initalization
Add unsafe set_len initialization
Add slow zero-filled vector initialization lint
Travis: Remove `sudo: false`
Downgrade needless_pass_by_value to allow by default
````