futures-core-preview broken on latest nightly

[tikue]

I think rust-lang/rust#54671 might have broken futures-core-preview when the std feature is enabled (which it is by default).

Lots of errors spit out, e.g.:

error[E0433]: failed to resolve. Could not find `std` in `{{root}}`                                                                                                                                                                                                                       
   --> futures-core/src/future/future_obj.rs:194:9                                                                                                                                                                                                                                        
    |                                                                                                                                                                                                                                                                                     
194 |     use std::boxed::Box;                                                                                                                                                                                                                                                            
    |         ^^^ Could not find `std` in `{{root}}` 

[cramertj]

Thanks for the report-- I'll have a PR up in a moment.