Make pipe work with PromiseProxies

- Relaxed the `instanceof` check to duck type if the object implements
  Promise-like methods to work with Objects that include the
  PromiseProxy mixin

addon/utils/is-promise.js

@@ -1,7 +1,13 @@
 import Ember from 'ember';
 
-const { RSVP: { Promise }, isPresent } = Ember;
+const { typeOf } = Ember;
+
+function isPromiseLike(obj = {}) {
+  return typeOf(obj.then) === 'function' &&
+    typeOf(obj.catch) === 'function' &&
+    typeOf(obj.finally) === 'function';
+}
 
 export default function isPromise(obj) {
-  return isPresent(obj) && obj instanceof Promise;
+  return typeOf(obj) === 'object' && isPromiseLike(obj);
 }

tests/unit/utils/is-promise-test.js

@@ -18,6 +18,10 @@ let testData = [
     value: new Promise((resolve) => resolve('blah')),
     expected: true
   },
+  {
+    value: { then: K, catch: K, finally: K },
+    expected: true
+  },
   {
     value: { then: K },
     expected: false
@@ -33,6 +37,10 @@ let testData = [
   {
     value: ['meow'],
     expected: false
+  },
+  {
+    value: null,
+    expected: false
   }
 ];