Optimize Promise v3 API compatibility to avoid hitting autoloader

src/functions.php

@@ -4,7 +4,6 @@
 
 use React\EventLoop\Loop;
 use React\EventLoop\LoopInterface;
-use React\Promise\CancellablePromiseInterface;
 use React\Promise\Promise;
 use React\Promise\PromiseInterface;
 
@@ -144,7 +143,7 @@ function timeout(PromiseInterface $promise, $time, LoopInterface $loop = null)
     // cancelling this promise will only try to cancel the input promise,
     // thus leaving responsibility to the input promise.
     $canceller = null;
-    if ($promise instanceof CancellablePromiseInterface || (!\interface_exists('React\Promise\CancellablePromiseInterface') && \method_exists($promise, 'cancel'))) {
+    if (\method_exists($promise, 'cancel')) {
         // pass promise by reference to clean reference after cancellation handler
         // has been invoked once in order to avoid garbage references in call stack.
         $canceller = function () use (&$promise) {
@@ -184,7 +183,7 @@ function timeout(PromiseInterface $promise, $time, LoopInterface $loop = null)
 
             // try to invoke cancellation handler of input promise and then clean
             // reference in order to avoid garbage references in call stack.
-            if ($promise instanceof CancellablePromiseInterface || (!\interface_exists('React\Promise\CancellablePromiseInterface') && \method_exists($promise, 'cancel'))) {
+            if (\method_exists($promise, 'cancel')) {
                 $promise->cancel();
             }
             $promise = null;

tests/FunctionTimeoutTest.php

@@ -64,6 +64,7 @@ public function testRejectedWillNotStartTimer()
     public function testPendingWillRejectOnTimeout()
     {
         $promise = $this->getMockBuilder('React\Promise\PromiseInterface')->getMock();
+        $promise->expects($this->once())->method('then')->willReturn($this->getMockBuilder('React\Promise\PromiseInterface')->getMock());
 
         $promise = Timer\timeout($promise, 0.01);