Update upload() chunk clean up condition.

[goodtimeaj]

In method upload() of class phpVimeo, if $use_multiple_chunks is true, then chunking will always create a file named my_upload_file.file_ext.0, and if $size of the main file is less than the chunking threshold then only one chunk will be created and this chunk will not be cleaned up after upload when the condition for deleting chunks is (count($chunks) > 1). So update the condition to be ($use_multiple_chunks) instead.