cargo test is broken on non-x86

[ignatenkobrain]

error[E0658]: use of unstable library feature 'stdsimd'
   --> tests/test.rs:394:29
    |
394 |                     let _ = is_x86_feature_detected!($feat);
    |                             ^^^^^^^^^^^^^^^^^^^^^^^
...
400 |     my_is_x86_feature_detected!("mmx");
    |     ----------------------------------- in this macro invocation
    |
    = note: see issue #27731 <https://github.com/rust-lang/rust/issues/27731> for more information
    = help: add `#![feature(stdsimd)]` to the crate attributes to enable
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: 
        is_x86_feature_detected can only be used on x86 and x86_64 targets.
        You can prevent it from being used in other architectures by
        guarding it behind a cfg(target_arch) as follows:
            #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] {
                if is_x86_feature_detected(...) { ... }
            }
        
   --> tests/test.rs:400:5
    |
400 |     my_is_x86_feature_detected!("mmx");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

This was fine on 0.1.14, but not on 0.1.15.

[dtolnay]

Sorry about that, fixed in 0.1.16.