使用geom_sf绘制空间对象时遇到麻烦。

nc <- sf::st_read(system.file("shape/nc.shp",package = "sf"),quiet = TRUE)

ggplot(nc) +
 geom_sf(aes(fill = AREA))

Error: 'st_normalize' is not an exported object from 'namespace:sf'

我在做什么错？这是版本问题吗？这是我的会话信息：

sessionInfo()
R version 3.5.0 (2018-04-23)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows >= 8 x64 (build 9200)

Matrix products: default

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252   
[3] LC_MONetaRY=English_United States.1252 LC_NUMERIC=C                          
[5] LC_TIME=English_United States.1252    

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

other attached packages:
 [1] sf_0.7-2        forcats_0.3.0   stringr_1.3.1   dplyr_0.8.3     purrr_0.3.3     readr_1.3.0    
 [7] tidyr_0.8.3     tibble_2.1.3    ggplot2_3.2.1   tidyverse_1.2.1

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.1           lubridate_1.7.4      lattice_0.20-35      class_7.3-14        
 [5] formula.tools_1.7.1  assertthat_0.2.0     zeallot_0.1.0        digest_0.6.18       
 [9] R6_2.3.0             cellranger_1.1.0     plyr_1.8.4           backports_1.1.3     
[13] e1071_1.7-0          spam_2.2-1           httr_1.4.0           pillar_1.4.2        
[17] rlang_0.4.0          lazyeval_0.2.1       readxl_1.2.0         rstudioapi_0.10     
[21] data.table_1.11.8    raster_2.8-4         Matrix_1.2-14        checkmate_1.8.5     
[25] rgdal_1.3-6          foreign_0.8-70       RCurl_1.95-4.11      munsell_0.5.0       
[29] broom_0.5.2          compiler_3.5.0       metR_0.5.0           modelr_0.1.2        
[33] pkgconfig_2.0.2      tidyselect_0.2.5     gridExtra_2.3        codetools_0.2-15    
[37] crayon_1.3.4         withr_2.1.2          bitops_1.0-6         grid_3.5.0          
[41] nlme_3.1-137         jsonlite_1.6         gtable_0.2.0         DBI_1.0.0           
[45] magrittr_1.5         units_0.6-2          scales_1.0.0         cli_1.1.0           
[49] stringi_1.2.4        sp_1.2-7             xml2_1.2.0           generics_0.0.2      
[53] vctrs_0.2.0          Formula_1.2-3        tools_3.5.0          glue_1.3.1          
[57] maps_3.3.0           hms_0.5.0            fields_9.6           yaml_2.2.0          
[61] colorspace_1.3-2     maptools_0.9-4       operator.tools_1.6.3 classInt_0.3-1      
[65] rvest_0.3.2          dotCall64_1.0-0      memoise_1.1.0        haven_2.0.0