DOC: Update minimum rust requirement to Rust 1.24

Rust 1.24 is on debian stable. It is compatible with crossbeam (Rust 1.26),
the rdep with most downloads.

Author: bluss

.travis.yml

@@ -4,13 +4,13 @@ env:
   - FEATURES='serde-1'
 matrix:
   include:
+    - rust: 1.24.1
+      env:
+      - FEATURES='array-sizes-33-128 array-sizes-129-255'
     - rust: stable
     - rust: stable
       env:
       - FEATURES='serde-1'
-    - rust: 1.22.1
-      env:
-      - FEATURES='array-sizes-33-128 array-sizes-129-255'
     - rust: stable
       env:
       - FEATURES='array-sizes-33-128 array-sizes-129-255'

src/lib.rs

@@ -16,7 +16,7 @@
 //!
 //! ## Rust Version
 //!
-//! This version of arrayvec requires Rust 1.13 or later.
+//! This version of arrayvec requires Rust 1.24 or later.
 //!
 #![doc(html_root_url="https://docs.rs/arrayvec/0.4/")]
 #![cfg_attr(not(feature="std"), no_std)]