Merge pull request #84 from digineo/go1.8

Test with Go 1.7.5 and 1.8.1

.travis.yml

@@ -2,7 +2,8 @@ language: go
 dist: trusty
 sudo: required
 go:
-  - 1.7.3
+  - 1.7.5
+  - 1.8.1
 env:
   - FTP_SERVER=vsftpd
   - FTP_SERVER=proftpd