libgimpmodule: include gio/gio.h for GFile
This fixes the gtk-doc build.
gmake[3]: Entering directory '/home/lantw44/gnome/build/gimp/devel-docs/libgimpmodule'
DOC Scanning header files
DOC Introspecting gobjects
In file included from libgimpmodule3-scan.c:8:
/home/lantw44/gnome/source/gimp/libgimpmodule/gimpmodule.h:190:52: error: unknown type name 'GFile'
GimpModule * gimp_module_new (GFile *file,
^
/home/lantw44/gnome/source/gimp/libgimpmodule/gimpmodule.h:194:1: error: unknown type name 'GFile'
GFile * gimp_module_get_file (GimpModule *module);
^
2 errors generated.