`Properties#store(OutputStream)` doesn't flush the output to the `OutputStream`

[gastaldi]

The following test fails:

 @Test
 void testStoreOutputStream() throws IOException, URISyntaxException {
 Path f = getResource("/test.properties");
 Properties p = Properties.loadProperties(f);
 ByteArrayOutputStream os = new ByteArrayOutputStream();
 p.store(os);
 assertThat(os.toString()).isEqualTo(readAll(f));
 }

Probably the OutputStreamWriter isn't flushing to the underlying OutputStream?