Travis: Test old rust versions
diff --git a/.travis.yml b/.travis.yml
index 73d986b..a058207 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,6 +2,10 @@
 sudo: false
 matrix:
   include:
+    - rust: 1.0.0
+    - rust: 1.1.0
+    - rust: 1.2.0
+    - rust: 1.3.0
     - rust: stable
     - rust: beta
     - rust: nightly