Missing append to file

[ivanmtw]

Trying write content to existing file, flags 'a' and 'w' so similar, and any write clear previously saved data:

$file = $filesystem->file($tsv_filename);
$file->open('ca')->then(function (React\Stream\WritableStreamInterface $stream) use ($tsv_data) {
$stream->write(implode("\t", $tsv_data) . "\n");
$stream->end();
echo "Data was written\n";
});

Apologize no file append functionality in reactphp/filesystem, please add it, thx.

[clue]

Resolved via #62. See appendContents().