fix nvm run with fresh capistrano

[vlad-gromov]

I have encountered weird errors like:

/tmp/my_project/nvm-exec.sh: line 5: /home/vlad/my_project/releases/20240530191133/RBENV_ROOT=/home/my_project/.rbenv: No such file or directory

Clearly something was wrong with the nvm-exec.sh file. Turns out it didn't work well with environment variables passed as arguments.

This small correction fixes that.