Move travis back to 1.28, since cc dependency is gone.

.travis.yml

@@ -0,0 +1,24 @@
+language: rust
+rust:
+  - nightly
+  - 1.28.0
+  - 1.49
+matrix:
+  allow_failures:
+    - rust: nightly
+  fast_finish: true
+script:
+- |
+  cargo build &&
+  cargo test
+env:
+  global:
+    secure: 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
+after_success: |
+  [ $TRAVIS_BRANCH = master ] &&
+  [ $TRAVIS_PULL_REQUEST = false ] &&
+  cargo doc &&
+  echo "<meta http-equiv=refresh content=0;url=`echo $TRAVIS_REPO_SLUG | cut -d '/' -f 2`/index.html>" > target/doc/index.html &&
+  sudo pip install ghp-import &&
+  ghp-import -n target/doc &&
+  git push -fq https://${GH_TOKEN}@github.com/${TRAVIS_REPO_SLUG}.git gh-pages