Fix invalid wikipedia url in AsyncWiki example

[karolrynio]

When I run AsyncWiki example i got exception because wikipedia url changed:

[info] Running AsyncWiki 
[error] (Thread-6) java.util.NoSuchElementException
java.util.NoSuchElementException
        at java.util.Scanner.throwFor(Scanner.java:862)
        at java.util.Scanner.next(Scanner.java:1371)
        at AsyncWiki$$anonfun$fetchWikipediaArticleAsynchronously$1$$anon$1$$anonfun$run$1.apply(AsyncWiki.scala:19)
        at AsyncWiki$$anonfun$fetchWikipediaArticleAsynchronously$1$$anon$1$$anonfun$run$1.apply(AsyncWiki.scala:14)
        at scala.collection.IndexedSeqOptimized$class.foreach(IndexedSeqOptimized.scala:33)
        at scala.collection.mutable.WrappedArray.foreach(WrappedArray.scala:35)
        at AsyncWiki$$anonfun$fetchWikipediaArticleAsynchronously$1$$anon$1.run(AsyncWiki.scala:14)
        at java.lang.Thread.run(Thread.java:745)

[zsxwing]

Thank you!