错误消息：open.connection 中的错误（路径，“wb”）：无法打开连接调用：... kable_as_image -> write_file-> open -> open.connection 执行暂停
使用以下命令编织 RMarkdown 文件时：
library(knitr)
library(kableExtra)
dt <- mtcars[1:5, 1:6]
options(knitr.table.format = "latex")
kable_as_image(kable_input = kable(dt),filename = "abcd",file_format =
"png",latex_header_includes = NULL, keep_pdf = FALSE)
工作目录：“C:/Users/xyz/Documents”
会话信息（）
R version 3.4.1 (2017-06-30)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows >= 8 x64 (build 9200)
Matrix products: default
locale:
[1] LC_COLLATE=English_India.1252 LC_CTYPE=English_India.1252
[3] LC_MONETARY=English_India.1252 LC_NUMERIC=C
[5] LC_TIME=English_India.1252
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] kableExtra_0.5.1
loaded via a namespace (and not attached):
[1] Rcpp_0.12.12 digest_0.6.12 rprojroot_1.2
[4] R6_2.2.2 backports_1.1.0 magrittr_1.5
[7] evaluate_0.10.1 httr_1.3.0 rlang_0.1.2
[10] stringi_1.1.5 magick_1.3 xml2_1.1.1
[13] rmarkdown_1.6.0.9004 tools_3.4.1 stringr_1.2.0
[16] readr_1.1.1 hms_0.3 yaml_2.1.14
[19] compiler_3.4.1 rvest_0.3.2 htmltools_0.3.6
[22] knitr_1.17 tibble_1.3.3