Attempt to use travis_wait to work around time outs:

> No output has been received in the last 10m0s, this potentially indicates
> a stalled build or something wrong with the build itself.

Author: SimonSapin

.travis.yml

@@ -8,7 +8,7 @@ rust:
 services:
   - docker
 script:
-  - if [[ $TRAVIS_RUST_VERSION = nightly* ]]; then
+  - travis_wait if [[ $TRAVIS_RUST_VERSION = nightly* ]]; then
       sh ci/run-travis.sh;
     else
       cargo build;