Fix pdflatex warning about multiple pdfs with page group.

Fix the following pdflatex warning:
pdfTeX warning: pdflatex (file ./fig/three_scenarios.pdf): PDF inclusion: multi
ple pdfs with page group included in a single page

File was fixed by the following command
mv fig/three_scenarios.pdf fig/three_scenarios.pdf~
gs -o fig/three_scenarios.pdf -sDEVICE=pdfwrite \
   -dColorConversionStrategy=/sRGB -dProcessColorModel=/DeviceRGB \
   fig/three_scenarios.pdf~

See
http://tex.stackexchange.com/questions/76273/multiple-pdfs-with-page-group-included-in-a-single-page-warning#78009