fix link formatting (#512)

economics/README.md

@@ -4,8 +4,8 @@
 
 * [Auctions and bidding: A guide for computer scientists (2011)](http://www.sci.brooklyn.cuny.edu/~parsons/projects/mech-design/publications/bluffers-final.pdf) by S. Parsons, J. Rodriguez-Aguilar, M. Klein
 
-* [Optimal Bidding in Online Auctions (2001)] (http://www.mit.edu/~dbertsim/papers/Revenue%20Management/Optimal%20Bidding%20in%20Online%20Auctions.pdf) by Dimitris Bertsimas, Jerey Hawkinsy, Georgia Perakis 
+* [Optimal Bidding in Online Auctions (2001)](http://www.mit.edu/~dbertsim/papers/Revenue%20Management/Optimal%20Bidding%20in%20Online%20Auctions.pdf) by Dimitris Bertsimas, Jerey Hawkinsy, Georgia Perakis 
 
 ## Open Source
 
-* [The Simple economics of Open Source  (2000)] (http://www.people.hbs.edu/jlerner/simple.pdf) by Josh Lerner and Jean Tirole
+* [The Simple economics of Open Source  (2000)](http://www.people.hbs.edu/jlerner/simple.pdf) by Josh Lerner and Jean Tirole