Nevermind, I got my expect script to work, and now Travis logs into particle-cli and compiles.
#!/usr/bin/expect
set timeout 10
set user [lindex $argv 0]
set password [lindex $argv 1]
spawn /home/travis/.nvm/v0.10.36/bin/particle cloud login
expect "? Please enter your email address: "
send "$user\r"
expect "? Please enter your password: "
send "$password\r"
interact
yay