fix travis build script

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index 5adcdbb..67e69c5 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,7 +4,7 @@
 matrix:
   include:
     - go: 1.5
-    - go: 1.10
+    - go: "1.10"
     - go: tip
   allow_failures:
     - go: tip