Update maintainer list.

libs/maintainers.txt

@@ -89,7 +89,7 @@ polygon               Lucanus Simonson <lucanus.j.simonson -at- intel.com>, Andr
 pool                  Stephen Cleary <scleary -at- jerviswebb.com>
 predef                Rene Rivera <grafikrobot -at- gmail.com>
 preprocessor          Paul Mensonides <pmenso57 -at- comcast.net>
-program_options       Vladimir Prus <ghost -at- cs.msu.su>
+program_options       Vladimir Prus <vladimir.prus -at- gmail.com>
 property_map          Douglas Gregor <dgregor -at- cs.indiana.edu>
 property_tree         Sebastian Redl <sebastian.redl -at- getdesigned.at>
 proto                 Eric Niebler <eric -at- boostpro.com>