Refactor: change "folder" to "directory" where needed.

This commit fixes every instance in which the word "folder" is
incorrectly used instead of "directory".

pages/common/sftp.md

@@ -20,9 +20,9 @@
 
 `put {{/path/local_file}}`
 
-- Transfer remote folder to the local system recursively (works with `put` too):
+- Transfer remote directory to the local system recursively (works with `put` too):
 
-`get -R {{/path/remote_folder}}`
+`get -R {{/path/remote_directory}}`
 
 - Get list of files on local machine: