Fix a couple dead links. (#517)

* Fix dead link for "On the resemblance and containment of documents"
* Fix dead link for "The operating system: should there be one?"
* Fix dead link for "Differential Privacy"
* Fix dead link for "A Theoretician's Guide to the Experimental Analysis of Algorithms"

clustering_algorithms/README.md

@@ -1,3 +1,3 @@
 ## Clustering Algorithms
 
-[On the resemblance and containment of documents](http://gatekeeper.dec.com/ftp/pub/dec/SRC/publications/broder/positano-final-wpnums.pdf) (Andrei Z. Broder)
+[On the resemblance and containment of documents](https://www.cs.princeton.edu/courses/archive/spr05/cos598E/bib/broder97resemblance.pdf) (Andrei Z. Broder)

experimental_algorithmics/README.md

@@ -5,4 +5,4 @@ It can be used in the analysis of algorithms [(Wikipedia)](http://en.wikipedia.o
 
 ## Included Papers
 
-* [:scroll:](a-theoreticians-guide-to-the-experimental-analysis-of-algorithms.pdf) [A Theoretician's Guide to the Experimental Analysis of Algorithms](http://davidsjohnson.net/papers/experguide.pdf) (David S. Johnson): An exceptionally well-written guide to correctly evaluating algorithms by experimental analysis. The techniques described in this paper do not only apply to theoreticians although the title might lead one to believe so. The examples used in this paper and specifically the method of listing straight-forward principles illustrated by pit-falls and pet peeves make for an excellent must-read for everyone intending to publish experimental algorithm results.
+* :scroll: [A Theoretician's Guide to the Experimental Analysis of Algorithms](a-theoreticians-guide-to-the-experimental-analysis-of-algorithms.pdf) (David S. Johnson): An exceptionally well-written guide to correctly evaluating algorithms by experimental analysis. The techniques described in this paper do not only apply to theoreticians although the title might lead one to believe so. The examples used in this paper and specifically the method of listing straight-forward principles illustrated by pit-falls and pet peeves make for an excellent must-read for everyone intending to publish experimental algorithm results.

information_theory/README.md

@@ -2,7 +2,7 @@
 
 * :scroll: [A Mathematical Theory of Communication](a-mathematical-theory-of-communication-1948.pdf)
 
-* [Differential Privacy](http://www.msr-waypoint.com/pubs/64346/dwork.pdf)
+* [Differential Privacy](https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/dwork.pdf)
   - How do we quantify the exposure an individual faces from being
     included in a statistical dataset?  How do we anonymize aggregated
     data in a way that has formal guarantees?

operating_systems/README.md

@@ -2,7 +2,7 @@
 
 * :scroll: [The UNIX Time-Sharing System](unix-time-sharing-system.pdf)
 
-* [The operating system: should there be one?](http://plosworkshop.org/2013/preprint/kell.pdf)
+* [The operating system: should there be one?](https://www.cl.cam.ac.uk/~srk31/research/papers/kell13operating.pdf)
 
 * [The Scalable Commutativity Rule: Designing Scalable Software for Multicore Processors](https://people.csail.mit.edu/nickolai/papers/clements-sc.pdf)