轴交点 - ggplot2

Question

我希望下面的图表（其中有负值）使水平轴与0处的垂直轴交叉。我已经跟随其他说使用expand命令的帖子，但这不起作用出于某种原因。

diff_votos <- structure(list(Grupo = c("Controle", "Tratado"), 
                             N = c(32271L, 7623L), 
                             diff_media = c(-0.3541 -0.4072), 
                             diff_sd = c(2.0513, 1.6324), 
                             Erro_padrao = c(0.0216, 0.0355)), 
                        .Names = c("Grupo", "N", 
                                   "diff_media", "diff_sd", "Erro_padrao"), 
                        class = c("tbl_df", "tbl", "data.frame"), 
                        row.names = c(NA, -2L))


ggplot(diff_votos, aes(x = Grupo, 
                       y = diff_media)) +
  geom_bar(position = position_dodge(), 
           stat = 'identity',
           colour = 'black',
           width = 0.5) +
  geom_errorbar(aes(ymin = diff_media - Erro_padrao,
                    ymax = diff_media + Erro_padrao),
                position = position_dodge(width = 0.9),
                width = 0.4,
                size = 0.5) +
  theme(legend.position = 'bottom',
        axis.title = element_text(size = 10),
        legend.text = element_text(size = 10),
        axis.text = element_text(size = 10),
        legend.title = element_text(size = 10)) +
  labs(x = 'Grupo', y = element_blank()) +
  scale_y_continuous(expand = c(0,0), limits = c(-0.6,0.6)) +
  theme_classic()