running `:RokuInstall` from a file in your current directory causes error

[entrez]

expected behavior

:RokuInstall should display a message like this on success:

compressing channel & uploading to roku (xx.xx.xx.xx)
application received: 639321 bytes stored. install success.

actual behavior

when run from a file in your current directory, its output includes an error message like this:

compressing channel & uploading to roku (xx.xx.xx.xx)
/Users/entrez/roku.vim/roku_scripts/install: line 59: cd: manifest: Not a directory application received: 639321 bytes stored. install success.

steps to reproduce the problem

1. open a Roku project file in vim or neovim with roku.vim installed:
   $ vim ~/channels/test/manifest
2. change the editor's current directory to the one containing the file:
   :cd %:p:h
3. run :RokuInstall or :RokuInstall <device>:
   :RokuInstall
4. see results

other information

shell version(s): bash v5.0.7, zsh v5.7.1, fish v3.0.2
vim version(s): vim v8.1.1900, neovim v0.3.7