Fix two broken links (#558)

* Fix broken link: PODC queues

* Fix broken link: p457-consolvo.pdf

data_structures/README.md

@@ -1,7 +1,7 @@
 # Data Structures
 
 * [Dynamic Hash Tables](http://www.csd.uoc.gr/~hy460/pdf/Dynamic%20Hash%20Tables.pdf)
-* [Simple, Fast, and Practical Non-Blocking and Blocking Concurrent Queue Algorithms](http://www.research.ibm.com/people/m/michael/podc-1996.pdf)
+* [Simple, Fast, and Practical Non-Blocking and Blocking Concurrent Queue Algorithms](https://www.cs.rochester.edu/u/scott/papers/1996_PODC_queues.pdf)
 * [RRB-Trees: Efficient Immutable Vectors](http://infoscience.epfl.ch/record/169879/files/RMTrees.pdf)
 * [Cuckoo Hashing](http://www.it-c.dk/people/pagh/papers/cuckoo-jour.pdf)
 * [Fenwick Tree](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.14.8917&rep=rep1&type=pdf)

gamification/README.md

@@ -4,7 +4,7 @@
 
 * [Defining Gamification - A Service Marketing Perspective](http://www.rolandhubscher.org/courses/hf765/readings/p17-huotari.pdf)
 
-* [Design Requirements for Technologies that Encourage Physical Activity](http://www.katherineeveritt.com/papers/p457-consolvo.pdf)
+* [Design Requirements for Technologies that Encourage Physical Activity](https://www.cs.helsinki.fi/u/thusu/opinnot/uschool/T-121.5500/p457-consolvo.pdf)
 
 * [Exploring the Potential of Gamification Among Frail Elderly Persons](http://gamification-research.org/wp-content/uploads/2011/04/12-Gerling.pdf)