Use rust 1.8.0 for testing

equal-l2 · equal-l2 · commit e73d1b26ed05 · 2017-06-07T21:59:41.000+09:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,4 +1,4 @@
 language: rust
 rust:
-  - 1.5.0
+  - 1.8.0
   - nightly

-Original file line number
+Diff line change
 language: rust
 rust:
 -  - 1.5.0
 +  - 1.8.0
   - nightly