Merge pull request aimacode#248 from Manthan-R-Sheth/fix_readme

Update the README of AIMA3e by fixing null references.

Author: ctjoreilly

README.md

@@ -30,7 +30,7 @@ Java implementation of algorithms from [Russell](http://www.cs.berkeley.edu/~rus
 |2.8|48|Reflex-Vacuum-Agent|[ReflexVacuumAgent](/aima-core/src/main/java/aima/core/environment/vacuum/ReflexVacuumAgent.java)|
 |2.10|49|Simple-Reflex-Agent|[SimpleReflexAgentProgram](/aima-core/src/main/java/aima/core/agent/impl/aprog/SimpleReflexAgentProgram.java)|
 |2.12|51|Model-Based-Reflex-Agent|[ModelBasedReflexAgentProgram](/aima-core/src/main/java/aima/core/agent/impl/aprog/ModelBasedReflexAgentProgram.java)|
-|3|66|Problem|[Problem](/aima-core/src/main/java/aima/core/search/framework/Problem.java)|
+|3|66|Problem|[Problem](/aima-core/src/main/java/aima/core/search/framework/problem/Problem.java)|
 |3.1|67|Simple-Problem-Solving-Agent|[SimpleProblemSolvingAgent](/aima-core/src/main/java/aima/core/search/framework/SimpleProblemSolvingAgent.java)|
 |3.2|68|Romania|[SimplifiedRoadMapOfPartOfRomania](/aima-core/src/main/java/aima/core/environment/map/SimplifiedRoadMapOfPartOfRomania.java)|
 |3.7|77|Tree-Search|[TreeSearch](/aima-core/src/main/java/aima/core/search/framework/qsearch/TreeSearch.java)|