adds Matthew Whitehead as a maintainer (hyperledger#5876)

* adds Matthew Whitehead as a maintainer

* alphabetizes list by github id

Signed-off-by: Justin Florentine <justin+github@florentine.us>

---------

Signed-off-by: Justin Florentine <justin+github@florentine.us>
Co-authored-by: Sally MacFarlane <macfarla.github@gmail.com>

MAINTAINERS.md

@@ -15,8 +15,8 @@
 | Daniel Lehrner   | daniellehrner    | daniellehrner    |
 | Diego López León | diega            | diega            |
 | Fabio Di Fabio   | fab-10           | fab-10           |
-| Gary Schulte     | garyschulte      | GarySchulte      | 
 | Gabriel Trintinalia | gabriel-trintinalia | gabrieltrintinalia |
+| Gary Schulte     | garyschulte      | GarySchulte      | 
 | Jiri Peinlich    | gezero           | JiriPeinlich     |
 | Gabriel Fukushima| gfukushima       | gfukushima       |
 | Justin Florentine| jflo             | RoboCopsGoneMad  |
@@ -25,6 +25,7 @@
 | Lucas Saldanha   | lucassaldanha    | lucassaldanha    |
 | Sally MacFarlane | macfarla         | macfarla         |
 | Karim Taam       | matkt            | matkt            |
+| Matthew Whitehead| matthew1001      | matthew.whitehead      |
 | Meredith Baxter  | mbaxter          | mbaxter          |
 | Stefan Pingel    | pinges           | pinges           |
 | Danno Ferrin     | shemnon          | shemnon          |