Auto merge of #175 - servo:jdm-patch-5, r=jdm

Use Xenial for TravisCI.

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Author: bors-servo

.travis.yml

@@ -4,7 +4,7 @@ rust:
   - beta
   - stable
 sudo: 9000
-dist: trusty
+dist: xenial
 os:
   - linux
   - osx
@@ -14,7 +14,7 @@ addons:
   apt:
     sources:
       - ubuntu-toolchain-r-test
-      - llvm-toolchain-trusty-5.0
+      - llvm-toolchain-xenial-5.0
     packages:
       - autoconf2.13
       - g++-6