fix compiler warning on array.into_iter()

[dmitris]

Fix the compile warnings listed below by changing into_iter() invocation to iter()
in the impl_zip_iter macro as recommended in rust-lang/rust#66145.
For additional background, see also rust-lang/rust#65819 and rust-lang/rust#66017 (the latter is the linter change producing the warning).

$ cargo build
   Compiling itertools v0.9.0 (/Users/dsavints/dev/hack/github.com/rust-itertools/itertools)
warning: this method call currently resolves to `<&[T; N] as IntoIterator>::into_iter` (due to autoref coercions), but that might change in the future when `IntoIterator` impls for arrays are added.
   --> src/ziptuple.rs:111:47
    |
111 |                 let size = *[$( $B.len(), )*].into_iter().min().unwrap();
    |                                               ^^^^^^^^^ help: use `.iter()` instead of `.into_iter()` to avoid ambiguity: `iter`
...
128 | impl_zip_iter!(A);
    | ------------------ in this macro invocation
    |
    = note: `#[warn(array_into_iter)]` on by default
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #66145 <https://github.com/rust-lang/rust/issues/66145>
    = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

warning: this method call currently resolves to `<&[T; N] as IntoIterator>::into_iter` (due to autoref coercions), but that might change in the future when `IntoIterator` impls for arrays are added.
   --> src/ziptuple.rs:111:47
    |
111 |                 let size = *[$( $B.len(), )*].into_iter().min().unwrap();
    |                                               ^^^^^^^^^ help: use `.iter()` instead of `.into_iter()` to avoid ambiguity: `iter`
...
129 | impl_zip_iter!(A, B);
    | --------------------- in this macro invocation
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #66145 <https://github.com/rust-lang/rust/issues/66145>
    = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

[phimuemue]

Looks good to me.

Thanks for keeping the formatting as is. Could you even sqash the commits into one?

@jswrenn I'd risk merging this even with CI failing, as CI nightly problems seem unrelated.

[dmitris]

Could you even squash the commits into one?

done

[jswrenn]

bors r+

[bors]

Build succeeded:

• continuous-integration/travis-ci/push