我正在构建一个软件包，每次通过devtools测试都很好，但我从Travis得到以下错误：
Building with: R CMD build
0.69s$ R CMD build .
* checking for file ‘./DESCRIPTION’ ... OK
* preparing ‘fars2’:
* checking DESCRIPTION meta-information ... OK
* installing the package to build vignettes
-----------------------------------
* installing *source* package ‘fars2’ ...
** R
** preparing package for lazy loading
Error in loadNamespace(j <- i[[1L]], c(lib.loc, .libPaths()), versionCheck = vI[[j]]) :
there is no package called ‘dplyr’
ERROR: lazy loading failed for package ‘fars2’
* removing ‘/tmp/RtmpUWHd2D/Rinst3a4038a68aec/fars2’
-----------------------------------
ERROR: package installation failed
我的描述文件：
Package: fars2
Type: Package
Title: Fatality Analysis Reporting System Data Manager
Version: 0.1.0
Author: Michael Conway
Maintainer: Michael Conway <mpconway@gmail.com>
Description: This package uploads, organizes and annalyzes Fatality Analysis Reporting System accident data.
License: GPL (>= 3)
Encoding: UTF-8
LazyData: true
Imports: dplyr,
readr,
tidyr,
maps,
graphics
Suggests: knitr,
rmarkdown,
testthat
VignetteBuilder: knitr
RoxygenNote: 6.0.1
有什么建议吗？