Bump go 1.6 dependencies, drop Go 1.6, add go 1.9, 1.12, 1.13 dependencies.

zhengchun · zhengchun · commit 2d52e1aaeb81 · 2020-01-11T12:18:50.000+08:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,9 +1,11 @@
 language: go
 
 go:
-  - 1.6
   - 1.7
   - 1.8
+  - 1.9.x
+  - 1.12.x
+  - 1.13.x
 
 install:
   - go get golang.org/x/net/html/charset
