Update library/src/uk/co/senab/photoview/PhotoViewAttacher.java

fix  ImageView no longer exists. You should not use this PhotoViewAttacher any more.
the cleanup don't work so i fixed it like this.

Author: xeodou

library/src/uk/co/senab/photoview/PhotoViewAttacher.java

@@ -176,8 +176,8 @@ public final boolean canZoom() {
 	 */
 	@SuppressWarnings("deprecation")
 	public final void cleanup() {
-		if (null != mViewTreeObserver && mViewTreeObserver.isAlive()) {
-			mViewTreeObserver.removeGlobalOnLayoutListener(this);
+		if (null != mImageView) {
+			mImageView.get().getViewTreeObserver().removeGlobalOnLayoutListener(this);
 		}
 		mViewTreeObserver = null;