Fix #6 File buffer not flushed

Download of small files fails with file size mismatch error.

The buffer of the download file was not flushed on download completion resulting in sporadic file size mismatch errors mostly on small file sizes.

Buffer is now flushed after the download.

campdown/helpers.py

@@ -387,6 +387,7 @@ def download_file(url, output, name, force=False, verbose=False, silent=False, s
 
                         # Flush the output buffer so we can overwrite the same line.
                         sys.stdout.flush()
+                f.flush()
 
                 # Verify our download size for completion. Since the file sizes will
                 # not entirely match up because of possible ID3 tag differences or