Add gio-2.0 and glib-2.0 to Require in generated .pc file

Looks like libgweather is using glib-2.0 and gio-2.0

$ find /usr/include/libgweather-4.0 -type f | xargs grep \#include | awk -F: '{print $2}' | sort| uniq

That patch fixes issue reported in evolution-data-server#385 (closed)