Add missing '@flow' and unify comments style

Author: IvanGoncharov

src/execution/index.js

@@ -1,3 +1,4 @@
+/* @flow */
 /**
  *  Copyright (c) 2015, Facebook, Inc.
  *  All rights reserved.

src/language/lexer.js

@@ -1,4 +1,4 @@
-/* @flow /
+/* @flow */
 /**
  *  Copyright (c) 2015, Facebook, Inc.
  *  All rights reserved.

src/subscription/asyncIteratorReject.js

@@ -1,12 +1,11 @@
+/* @flow */
 /**
  * Copyright (c) 2017, Facebook, Inc.
  * All rights reserved.
  *
  * This source code is licensed under the BSD-style license found in the
  * LICENSE file in the root directory of this source tree. An additional grant
  * of patent rights can be found in the PATENTS file in the same directory.
- *
- * @flow
  */
 
 import { $$asyncIterator } from 'iterall';

src/subscription/index.js

@@ -1,12 +1,11 @@
+/* @flow */
 /**
  * Copyright (c) 2017, Facebook, Inc.
  * All rights reserved.
  *
  * This source code is licensed under the BSD-style license found in the
  * LICENSE file in the root directory of this source tree. An additional grant
  * of patent rights can be found in the PATENTS file in the same directory.
- *
- * @flow
  */
 
 export { subscribe, createSourceEventStream } from './subscribe';

src/subscription/mapAsyncIterator.js

@@ -1,12 +1,11 @@
+/* @flow */
 /**
  * Copyright (c) 2017, Facebook, Inc.
  * All rights reserved.
  *
  * This source code is licensed under the BSD-style license found in the
  * LICENSE file in the root directory of this source tree. An additional grant
  * of patent rights can be found in the PATENTS file in the same directory.
- *
- * @flow
  */
 
 import { $$asyncIterator, getAsyncIterator } from 'iterall';

src/subscription/subscribe.js

@@ -1,12 +1,11 @@
+/* @flow */
 /**
  * Copyright (c) 2017, Facebook, Inc.
  * All rights reserved.
  *
  * This source code is licensed under the BSD-style license found in the
  * LICENSE file in the root directory of this source tree. An additional grant
  * of patent rights can be found in the PATENTS file in the same directory.
- *
- * @flow
  */
 
 import { isAsyncIterable } from 'iterall';

src/validation/index.js

@@ -1,3 +1,4 @@
+/* @flow */
 /**
  *  Copyright (c) 2015, Facebook, Inc.
  *  All rights reserved.