chore: test against 1.15 and 1.16

Author: thinkingserious

.travis.yml

@@ -1,15 +1,7 @@
 language: go
 go:
-- 1.7.x
-- 1.8.x
-- 1.9.x
-- 1.10.x
-- 1.11.x
-- 1.12.x
-- 1.13.x
-- 1.14.x
-- 1.15.x
-- tip
+- 1.15
+- 1.16
 script:
 - make test
 - "./go.test.sh"