travis: Use Go 1.11 and 1.12
diff --git a/.travis.yml b/.travis.yml
index fc3936b..0504cf2 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -7,9 +7,8 @@
     - GO15VENDOREXPERIMENT=1
 
 go:
-  - 1.7
-  - 1.8
-  - 1.9
+  - 1.11.x
+  - 1.12.x
 
 cache:
   directories: