Fix recursion when listing directories

Sftp::scanDirectory() always recursively scans a whole directory tree even if no recursion is wanted. This patch uses scandir instead of the recursive method-call to avoid this.
Merge branch 'master' from Herzult/php-ssh into sft-recursion-fix
Fix .travis.yml
Fix .travis.yml
Merge pull request #20 from woiwa/sft-recursion-fix

Fix recursion when listing directories.