Auto merge of #229 - brendanzab:pin-rustc-version, r=KiChjang

Pin rustc version in .travis.yml

This ensures that we test against Rust 1.36 in CI on all builds. This is very helpful documentation for downstream maintainers, as it quickly helps us figure out what version of Rust is supported by the library, and highlights changes to the minimum supported version during code review.

Closes #228.

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Author: bors-servo

.travis.yml

@@ -1,6 +1,7 @@
 sudo: false
 language: rust
 rust:
+  - 1.36.0
   - nightly
   - beta
   - stable