Drop golang 1.6 from official support

.travis.yml

@@ -1,6 +1,5 @@
 language: go
 go:
-- 1.6.3
 - 1.7.3
 - 1.8
 

README.md

@@ -20,7 +20,7 @@ You might also want to look at the [Frequently Asked Questions](https://github.c
 Sarama provides a "2 releases + 2 months" compatibility guarantee: we support
 the two latest stable releases of Kafka and Go, and we provide a two month
 grace period for older releases. This means we currently officially support
-Go 1.8, 1.7, and 1.6, and Kafka 0.10 and 0.9, although older releases are
+Go 1.8 and 1.7, and Kafka 0.10 and 0.9, although older releases are
 still likely to work.
 
 Sarama follows semantic versioning and provides API stability via the gopkg.in service.