Update MSRV to 1.39.0, fix doc test that fails <1.41.0.

Author: adamgreig

cortex-m-rt/.travis.yml

@@ -4,24 +4,24 @@ matrix:
   allow_failures:
     - rust: nightly
   include:
-    # MSRV 1.32.0 #############################################################
+    # MSRV 1.39.0 #############################################################
     - env: TARGET=x86_64-unknown-linux-gnu
-      rust: 1.32.0
+      rust: 1.39.0
 
     - env: TARGET=thumbv6m-none-eabi
-      rust: 1.32.0
+      rust: 1.39.0
 
     - env: TARGET=thumbv7m-none-eabi
-      rust: 1.32.0
+      rust: 1.39.0
 
     - env: TARGET=thumbv7em-none-eabi
-      rust: 1.32.0
+      rust: 1.39.0
 
     - env: TARGET=thumbv7em-none-eabihf
-      rust: 1.32.0
+      rust: 1.39.0
 
     - env: TARGET=thumbv8m.main-none-eabi
-      rust: 1.32.0
+      rust: 1.39.0
 
     # Stable ##################################################################
     - env: TARGET=x86_64-unknown-linux-gnu

cortex-m-rt/src/lib.rs

@@ -372,6 +372,7 @@
 //! [`MaybeUninit`]: https://doc.rust-lang.org/core/mem/union.MaybeUninit.html
 //!
 //! ```no_run,edition2018
+//! # extern crate core;
 //! use core::mem::MaybeUninit;
 //!
 //! const STACK_SIZE: usize = 8 * 1024;
@@ -391,7 +392,7 @@
 //!
 //! # Minimum Supported Rust Version (MSRV)
 //!
-//! The MSRV of this release is Rust 1.32.0.
+//! The MSRV of this release is Rust 1.39.0.
 
 // # Developer notes
 //