remove golang 1.7 support

Author: ringtail

.travis.yml

@@ -2,11 +2,10 @@ language: go
 install: true
 sudo: required
 go:
-  - 1.7
   - 1.8
   - 1.9
   - master
 script:
   - ./test.sh
 after_success:
-  - bash <(curl -s https://codecov.io/bash)
+  - bash <(curl -s https://codecov.io/bash)