Matpower manual: typo in gurobi section (#214)

docs/src/MATPOWER-manual/MATPOWER-manual.tex

@@ -7464,7 +7464,7 @@ \subsection{\gurobi{} -- High-performance LP, QP, MILP and MIQP Solvers}
 
 \gurobi{}~\cite{gurobi} is a collection of optimization tools that includes high-performance solvers for large-scale linear programming (LP) and quadratic programming (QP) problems, among others. The project was started by some former \cplex{} developers. More information is available at \url{https://www.gurobi.com/}.
 
-Although \gurobi{} is a commercial package, at the time of this writing their is a free academic license available. See \url{https://www.gurobi.com/academia/for-universities} for more details.
+Although \gurobi{} is a commercial package, at the time of this writing there is a free academic license available. See \url{https://www.gurobi.com/academia/for-universities} for more details.
 
 Beginning with version~5.0.0, \gurobi{} includes a native \matlab{} interface, which is supported in \matpower{} version~4.2 and above.\footnote{\matpower{} version~4.1 supported \gurobi{} version 4.x, which required a free third-party \matlab{} MEX interface \cite{gurobimex}, available at \url{http://www.convexoptimization.com/wikimization/index.php/Gurobi_mex}.}