Fix typo in README (#155)

Author: odow

README.md

@@ -91,7 +91,7 @@ Query the number of scalar subproblems that were solved using
 
 ## Solution ordering
 
-Results are lexicograhically ordered by their objective vectors. The order
+Results are lexicographically ordered by their objective vectors. The order
 depends on the objective sense. The first result is best.
 
 ## Ideal point