Update list of maintainers (#164)

Author: odow

pages/maintainers.md

@@ -68,8 +68,12 @@ This document lists community members who are [repository maintainers](/pages/go
   - [MutableArithmetics.jl](https://github.com/jump-dev/MutableArithmetics.jl)
 * Simon Bowly (@simonbowly)
   - [Gurobi.jl](https://github.com/jump-dev/Gurobi.jl)
+* Stevenn G. Johnsonn (@stevengj)
+  - [NLopt.jl](https://github.com/jump-dev/NLopt.jl)
 * Tomás Gutierrez (@tomasfmg)
   - [ParametricOptInterface.jl](https://github.com/jump-dev/ParametricOptInterface.jl)
+* Truls Flatberg (@trulsf)
+  - [PiecewiseLinearOpt.jl](https://github.com/jump-dev/PiecewiseLinearOpt.jl)
 * David Torres (@torressa)
   - [Gurobi.jl](https://github.com/jump-dev/Gurobi.jl)
 * Yeesian Ng (@yeesian)