travis: update rust to 2019-03-19 nightly for 1.35

Author: rubdos

.travis.yml

@@ -2,7 +2,7 @@ language: rust
 cache: cargo
 
 rust:
-  - nightly-2018-12-31
+  - nightly-2019-03-19
 
 env:
   - TEST_COMMAND=test EXTRA_FLAGS='' FEATURES=''
@@ -14,7 +14,7 @@ env:
 matrix:
   fast_finish: true
   include:
-  - rust: nightly-2018-12-31
+  - rust: nightly-2019-03-19
     before_script:
     - rustup component add rustfmt-preview
     script: