Use onWritable watcher instead of repeat

The behavior of repeat with a 0 timeout is unpredictable in various loop implementations.

Author: trowski

src/Test.php

@@ -1224,16 +1224,16 @@ function testDeferEnabledInNextTick() {
 
         $invoked = 0;
 
-        $repeat = $this->loop->repeat($delay = 0, function () use (&$invoked) {
+        $watcher = $this->loop->onWritable(STDOUT, function () use (&$invoked) {
             $invoked++;
         });
 
         $tick();
         $tick();
         $tick();
 
-        $this->loop->disable($repeat);
-        $this->loop->enable($repeat);
+        $this->loop->disable($watcher);
+        $this->loop->enable($watcher);
         $tick(); // disable + immediate enable after a tick should have no effect either
 
         $this->assertEquals(4, $invoked);