fix compile issue with gtk 2.20 and bump depend to gtk/glib 2.20
fix compile issue with gtk 2.20 and bump depend to gtk/glib 2.20

tonyolag/gummi-vim,jmarshallnz/gummi,jmarshallnz/gummi,tonyolag/gummi-vim,tonyolag/gummi-vim,jmarshallnz/gummi,jmarshallnz/gummi,tonyolag/gummi-vim