问无法运行flexdashboard示例代码-

EN

Error in switch(options$dev, pdf = ".pdf", jpeg = ".jpeg", ".png") : 
EXPR must be a length 1 vector Calls: <Anonymous> ... fun -> 
withVisible -> knit_print -> html_screenshot

R version 3.3.1 (2016-06-21)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 7 x64 (build 7601) Service Pack 1

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252    LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C                           LC_TIME=English_United States.1252    

attached base packages:
[1] grid      stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] maps_3.2.0          bindrcpp_0.2        highcharter_0.5.0   quantmod_0.4-12     TTR_0.23-3         
[6] xts_0.10-0          zoo_1.8-0           formattable_0.2.0.1 officer_0.2.1       flextable_0.4.2    
[11] gridExtra_2.3       knitr_1.17          kableExtra_0.7.0    dplyr_0.7.4         lubridate_1.6.0    
[16] rstudioapi_0.7      RODBC_1.3-15        plotly_4.7.1        ggplot2_2.2.1      

loaded via a namespace (and not attached):
[1] httr_1.3.1          tidyr_0.7.2         jsonlite_1.5            viridisLite_0.2.0   R.utils_2.6.0      
[6] shiny_1.0.5         assertthat_0.2.0    yaml_2.1.16         gdtools_0.1.6       backports_1.1.1    
[11] lattice_0.20-35     glue_1.1.1          rlist_0.4.6.1         uuid_0.1-2          digest_0.6.12      
[16] rvest_0.3.2         colorspace_1.3-2    htmltools_0.3.6     httpuv_1.3.5        R.oo_1.21.0        
[21] plyr_1.8.4          psych_1.7.8         pkgconfig_2.0.1     broom_0.4.2         flexdashboard_0.5.1
[26] purrr_0.2.3         xtable_1.8-2        scales_0.5.0        tibble_1.3.4        lazyeval_0.2.0     
[31] mnormt_1.5-5        magrittr_1.5        mime_0.5            evaluate_0.10.1     R.methodsS3_1.7.1  
[36] nlme_3.1-131        xml2_1.1.1          foreign_0.8-69      tools_3.3.1         data.table_1.10.4  
[41] hms_0.3             stringr_1.2.0       munsell_0.4.3       zip_1.0.0           rlang_0.1.2        
[46] htmlwidgets_1.0     crosstalk_1.0.0     igraph_1.1.2        base64enc_0.1-3     labeling_0.3       
[51] rmarkdown_1.6       gtable_0.2.0        curl_3.0            reshape2_1.4.2      R6_2.2.2           
[56] bindr_0.1           rprojroot_1.2       readr_1.1.1         stringi_1.1.5       parallel_3.3.1     
[61] Rcpp_0.12.12        tidyselect_0.2.0