Auto merge of #62 - mrobinson:pin-travis, r=metajack

Pin travis to the 2015-07-10 rust nightly

This is a temporary work-around for an incompatibility between the
latest version of aster and the current rust nightly.

<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/servo/skia/62)
<!-- Reviewable:end -->

Author: bors-servo

.travis.yml

@@ -1,6 +1,10 @@
 sudo: false
 language: rust
-rust: nightly
+
+# We pin rust here, because aster (0.3.3) is broken with the latest
+# rust nightly. Once aster is fixed we can change this back to 'nightly.'
+rust: nightly-2015-07-10
+
 branches:
   except:
     - master