Add 1.3 to Travis' build matrix

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index 0c442b5..6012180 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,4 +3,5 @@
 go:
     - 1.1
     - 1.2
+    - 1.3
     - tip