add .travis.yml to at least build and run (nonexistent) tests

Author: nikomatsakis

.travis.yml

@@ -0,0 +1,14 @@
+language: rust
+before_script:
+- rustup component add rustfmt-preview
+rust:
+- beta
+- nightly
+matrix:
+- fast_finish: true
+- allow_failures:
+  - nightly
+script:
+- cargo build
+- cargo fmt --all -- --check
+- cargo test --all