去掉不必要的线(轴？)在Choroplethr中

Question

每当我使用Choroplethr包进行一次合唱时，就会出现这些不必要的代码行。我相信它们是轴，但是state_choropleth函数不应该是打印轴。

示例：

df <- data.frame(region = c("alabama", "alaska", "arizona", "arkansas", "california", "colorado", "connecticut", "delaware", "district of columbia", "florida", "georgia", "hawaii", "idaho", "illinois", "indiana", "iowa", "kansas", "kentucky", "louisiana", "maine", "maryland", "massachusetts", "michigan", "minnesota", "mississippi", "missouri", "montana", "nebraska", "nevada", "new hampshire", "new jersey", "new mexico", "new york", "north carolina", "north dakota", "ohio", "oklahoma", "oregon", "pennsylvania", "rhode island", "south carolina", "south dakota", "tennessee", "texas", "utah", "vermont", "virginia", "washington", "west virginia", "wisconsin", "wyoming"), value = runif(51))
state_choropleth(df)

这就是结果：Map with extraneous lines

有人能帮我摆脱这些吗？我仔细查看了Choroplethr的源代码，但似乎找不出它们是什么。

编辑:我运行的是Windows10Enterprise，R 3.4.2 64位，并且已经安装了choroplethr 3.6.1和ggplot2 2.2.1。