title: Cannot install an R package from Github
body: <p>I'm trying to run <code>devtools::install_github("gaborcsardi/notifier")</code> but R does not appear to be properly recognizing RTools; which is located in <code>C:\Rtools</code>.</p>
  
  <p>After following the instructions on <a href="https://github.com/r-lib/devtools/issues/1772" rel="noreferrer">https://github.com/r-lib/devtools/issues/1772</a>, running <code>pkgbuild::find_rtools()</code> still gives me the following error using the CRAN version of <code>devtools</code> and <code>pkgbuild</code>:</p>
  
  <p><code>Error in rethrow_call(c_processx_exec, command, c(command, args), stdin,  : 
    Command not found @win/processx.c:977</code></p>
  
  <p>Here is my <code>session_info()</code>:</p>
  
  <pre><code>- Session info ----------------------------------------------------------------------------------------------------------
   setting  value                       
   version  R version 3.5.2 (2018-12-20)
   os       Windows 10 x64              
   system   x86_64, mingw32             
   ui       RStudio                     
   language (EN)                        
   collate  English_United States.1252  
   ctype    English_United States.1252  
   tz       America/Chicago             
   date     2019-09-03                  
  
  - Packages --------------------------------------------------------------------------------------------------------------
   ! package         * version   date       lib source        
     assertthat        0.2.1     2019-03-21 [1] CRAN (R 3.5.3)
     backports         1.1.4     2019-04-10 [1] CRAN (R 3.5.3)
     bindr             0.1.1     2018-03-13 [2] CRAN (R 3.5.2)
     bindrcpp          0.2.2     2018-03-29 [2] CRAN (R 3.5.2)
     bit               1.1-14    2018-05-29 [1] CRAN (R 3.5.2)
     bit64             0.9-7     2017-05-08 [1] CRAN (R 3.5.2)
     blob              1.1.1     2018-03-25 [1] CRAN (R 3.5.3)
     callr             3.3.1     2019-07-18 [1] CRAN (R 3.5.3)
     cellranger        1.1.0     2016-07-27 [2] CRAN (R 3.5.2)
     cli               1.1.0     2019-03-19 [1] CRAN (R 3.5.3)
     crayon            1.3.4     2017-09-16 [1] CRAN (R 3.5.3)
     curl              3.3       2019-01-10 [1] CRAN (R 3.5.3)
     data.table        1.12.2    2019-04-07 [1] CRAN (R 3.5.3)
     DBI               1.0.0     2018-05-02 [1] CRAN (R 3.5.3)
     desc              1.2.0     2018-05-01 [1] CRAN (R 3.5.3)
     devtools        * 2.1.0     2019-07-06 [1] CRAN (R 3.5.3)
     digest            0.6.19    2019-05-20 [1] CRAN (R 3.5.3)
     dplyr           * 0.7.8     2018-11-10 [1] CRAN (R 3.5.2)
     fs                1.3.1     2019-05-06 [1] CRAN (R 3.5.3)
   D glue              1.3.1     2019-03-12 [1] CRAN (R 3.5.3)
     hms               0.4.2     2018-03-10 [1] CRAN (R 3.5.3)
     httr            * 1.4.0     2018-12-11 [2] CRAN (R 3.5.2)
     jsonlite          1.6       2018-12-07 [2] CRAN (R 3.5.2)
     lubridate       * 1.7.4     2018-04-11 [2] CRAN (R 3.5.2)
     magrittr          1.5       2014-11-22 [1] CRAN (R 3.5.3)
     mailR           * 0.4.1     2015-01-14 [1] CRAN (R 3.5.3)
     memoise           1.1.0     2017-04-21 [2] CRAN (R 3.5.2)
     odbc            * 1.1.6     2018-06-09 [1] CRAN (R 3.5.2)
     packrat           0.5.0     2018-11-14 [1] CRAN (R 3.5.3)
     pillar            1.4.1     2019-05-28 [1] CRAN (R 3.5.3)
     pkgbuild        * 1.0.5     2019-08-26 [1] CRAN (R 3.5.3)
     pkgconfig         2.0.2     2018-08-16 [1] CRAN (R 3.5.3)
     pkgload           1.0.2     2018-10-29 [1] CRAN (R 3.5.3)
     plyr              1.8.4     2016-06-08 [2] CRAN (R 3.5.2)
     prettyunits       1.0.2     2015-07-13 [1] CRAN (R 3.5.3)
     processx        * 3.4.1     2019-07-18 [1] CRAN (R 3.5.3)
     ps                1.3.0     2018-12-21 [1] CRAN (R 3.5.3)
     purrr             0.3.2     2019-03-15 [1] CRAN (R 3.5.3)
     R.methodsS3       1.7.1     2016-02-16 [1] CRAN (R 3.5.2)
     R.oo              1.22.0    2018-04-22 [1] CRAN (R 3.5.2)
     R.utils           2.8.0     2019-02-14 [1] CRAN (R 3.5.3)
     R6                2.4.0     2019-02-14 [1] CRAN (R 3.5.3)
     Rcpp              1.0.1     2019-03-17 [1] CRAN (R 3.5.3)
     RDCOMClient     * 0.93-0    2018-04-28 [1] local         
     readxl          * 1.3.1     2019-03-13 [1] CRAN (R 3.5.3)
     rematch           1.0.1     2016-04-21 [2] CRAN (R 3.5.2)
     remotes           2.1.0     2019-06-24 [1] CRAN (R 3.5.3)
     reshape         * 0.8.8     2018-10-23 [1] CRAN (R 3.5.3)
   D rJava             0.9-11    2019-03-29 [1] CRAN (R 3.5.3)
     rlang             0.4.0     2019-06-25 [1] CRAN (R 3.5.3)
     rprojroot         1.3-2     2018-01-03 [2] CRAN (R 3.5.2)
     rstudioapi        0.10      2019-03-19 [1] CRAN (R 3.5.3)
     rvest           * 0.3.4     2019-05-15 [1] CRAN (R 3.5.3)
     sessioninfo       1.1.1     2018-11-05 [1] CRAN (R 3.5.3)
     splitstackshape * 1.4.8     2019-04-21 [1] CRAN (R 3.5.3)
     stringi           1.4.3     2019-03-12 [1] CRAN (R 3.5.3)
     stringr           1.4.0     2019-02-10 [1] CRAN (R 3.5.3)
   D testthat          2.1.1     2019-04-23 [1] CRAN (R 3.5.3)
     tibble            2.1.1     2019-03-16 [1] CRAN (R 3.5.3)
     tidyr           * 0.8.3     2019-03-01 [1] CRAN (R 3.5.3)
     tidyselect        0.2.5     2018-10-11 [1] CRAN (R 3.5.3)
     usethis         * 1.5.0     2019-04-07 [1] CRAN (R 3.5.3)
     withr             2.1.2     2018-03-15 [1] CRAN (R 3.5.3)
     writexl         * 1.1       2018-12-02 [2] CRAN (R 3.5.2)
     XML             * 3.98-1.19 2019-03-06 [1] CRAN (R 3.5.2)
     xml2            * 1.2.0     2018-01-24 [1] CRAN (R 3.5.3)
  
  [1] \\termna.local/Shares/User Shares/Kyle.Dixon/Documents/R/win-library/3.5
  [2] \\termna.local/Shares/User Shares/Kyle.Dixon/Documents/R/R-3.5.2/library
  
   D -- DLL MD5 mismatch, broken installation.
  </code></pre>