Travis: Add minimum support Rust version and 32-bit support

Author: chansuke

.travis.yml

@@ -10,6 +10,7 @@ rust:
   - nightly
   - beta
   - stable
+  - 1.13.0
 os:
   - linux
   - osx
@@ -26,8 +27,12 @@ script:
         popd;
     done
   - ./test-scripts/check-copyright-comments.sh
+  - curl -sSL https://raw.githubusercontent.com/carllerche/travis-rust-matrix/master/test | bash
 
 env:
   global:
     # Override the default `--features unstable` used for the nightly branch
     - TRAVIS_CARGO_NIGHTLY_FEATURE=""
+    - ARCH=x86_64
+    - ARCH=i686
+