Rollup merge of rust-lang#66797 - mlodato517:mlodato517-array-doc-typo, r=Dylan-DPC

Fixes small typo in array docs r? @steveklabnik

Fixes a small typo in the array documentation.

Also, wasn't sure which [message](https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#pull-requests) to put this in, and will definitely update the commit message if it is supposed to be the PR description but for "safety" - r? @steveklabnik

Author: tmandry

src/libcore/array/mod.rs

@@ -1,5 +1,5 @@
 //! Implementations of things like `Eq` for fixed-length arrays
-//! up to a certain length. Eventually we should able to generalize
+//! up to a certain length. Eventually, we should be able to generalize
 //! to all lengths.
 //!
 //! *[See also the array primitive type](../../std/primitive.array.html).*