remove go 1.9-1.12 from testing, add go 1.14 (#25)

Author: isopov

.travis.yml

@@ -2,8 +2,5 @@ language: go
 
 go:
   - "1.8.x"
-  - "1.9.x"
-  - "1.10.x"
-  - "1.11.x"
-  - "1.12.x"
+  - "1.14.x"
   - tip