pin to an older nightly

Jorge Aparicio · Jorge Aparicio · commit d6f953458d3a · 2017-03-11T21:08:59.000-05:00
cf rust-lang/cargo#3819
diff --git a/.travis.yml b/.travis.yml
@@ -1,6 +1,6 @@
 dist: trusty
 language: rust
-rust: nightly
+rust: nightly-2017-03-04
 services: docker
 sudo: required
 
