Fix link to yield-from.pdf

Author: samtygier

content/extra/classic-coroutines/index.adoc

@@ -1277,7 +1277,7 @@ David Beazley is the ultimate authority on Python generators and coroutines. The
 
 Coroutines allow new ways of organizing code, and just as recursion or polymorphism (dynamic dispatch), it takes some time getting used to their possibilities. An interesting example of classic algorithm rewritten with coroutines is in the post http://bit.ly/1HGsFQ0["Greedy algorithm with coroutines,"] by James Powell. You may also want to browse http://bit.ly/1HGsFzA["Popular recipes tagged _coroutine_"] in the ActiveState Code https://code.activestate.com/recipes/[recipes database].
 
-Paul Sokolovsky implemented `yield from` in Damien George's super lean http://micropython.org[MicroPython] interpreter designed to run on microcontrollers. As he studied the feature, he created a http://bit.ly/1JIqGxW[great, detailed diagram] to explain how `yield from` works, and shared it in the python-tulip mailing list. Sokolovsky was kind enough to allow me to copy the PDF to this book's site, where it has a https://www.fluentpython.com/content/extra/classic-coroutines/images/yield-from.pdf[more permanent URL].
+Paul Sokolovsky implemented `yield from` in Damien George's super lean http://micropython.org[MicroPython] interpreter designed to run on microcontrollers. As he studied the feature, he created a http://bit.ly/1JIqGxW[great, detailed diagram] to explain how `yield from` works, and shared it in the python-tulip mailing list. Sokolovsky was kind enough to allow me to copy the PDF to this book's site, where it has a https://www.fluentpython.com/extra/classic-coroutines/images/yield-from.pdf[more permanent URL].
 
 As I write this, the vast majority of uses of `yield from` to be found are in `asyncio` itself or code that uses it. I spent a lot of time looking for examples of `yield from` that did not depend on `asyncio`. Greg Ewing--who penned PEP 380 and implemented `yield from` in CPython--published http://bit.ly/1JIqJtu[a few examples] of its use: a `BinaryTree` class, a simple XML parser, and a task scheduler.