use nightly

.travis.yml

 # Based on the "trust" template v0.1.2
 # https://github.com/japaric/trust/tree/v0.1.2
 
-dist: trusty
 language: rust
 services: docker
-sudo: required
 
 matrix:
   include:
     # Linux
     - env: TARGET=x86_64-unknown-linux-gnu
+      rust: nightly
 
     # Bare metal
     - env: TARGET=thumbv7em-none-eabi
+      rust: nightly
     - env: TARGET=thumbv7em-none-eabihf
+      rust: nightly
 
 before_install:
   - set -e