Incorrect hints from trivial_regex for bytes regexes

[jeltz]

The trivial_regex lint does not seem to make any difference between regex::Regex and regex::bytes::Regex when giving hints. I am not sure what should be used for non-anchored regexes, maybe the memchr crate, for anchored it should suggest slice::starts_with and slice::ends_with.

warning: trivial regex                                                                                   
 --> src/bin/foo.rs:2:30                                                                                 
  |                                                                                                      
2 |     regex::bytes::Regex::new("foo").unwrap();                                                        
  |                              ^^^^^                                                                   
  |                                                                                                      
  = note: #[warn(clippy::trivial_regex)] on by default                                                   
  = help: consider using `str::contains`                                                                 
  = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/master/index.html#trivial_regex
                                                                                                         
warning: trivial regex                                                                                   
 --> src/bin/foo.rs:3:30                                                                                 
  |                                                                                                      
3 |     regex::bytes::Regex::new("^bar").unwrap();                                                       
  |                              ^^^^^^                                                                  
  |                                                                                                      
  = help: consider using `str::starts_with`                                                              
  = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/master/index.html#trivial_regex

Version: clippy 0.0.212 (2e26fdc 2018-11-22)