Update dependencies

Among others, this updates minio-go, so that the new "eu-west-3" zone
for AWS is supported.

vendor/github.com/pkg/sftp/.travis.yml

@@ -1,10 +1,11 @@
 language: go
 go_import_path: github.com/pkg/sftp
 
-# current and previous stable releases, and tip
+# current and previous stable releases, plus tip
+# remember to exclude previous and tip for macs below
 go:
-  - 1.7.x
   - 1.8.x
+  - 1.9.x
   - tip
 
 os:
@@ -14,7 +15,7 @@ os:
 matrix:
   exclude:
     - os: osx
-      go: 1.7.x
+      go: 1.8.x
     - os: osx
       go: tip