assume-role doesn't work if your AWS environment variables are already set

[veqryn]

I have the main two aws environment variables already set:

MinGW 04:43:03 ~$ printenv | sort | grep AWS
AWS_ACCESS_KEY_ID=xxx
AWS_SECRET_ACCESS_KEY=xxx

When I run assume-role, it doesn't ask for my MFA and it just spits out the current variables:

MinGW 04:43:06 ~$ assume-role.exe eo
$env:AWS_ACCESS_KEY_ID="xxx"
$env:AWS_SECRET_ACCESS_KEY="xxx"
$env:AWS_SESSION_TOKEN=""
$env:AWS_SECURITY_TOKEN=""
$env:ASSUMED_ROLE="eo"
# Run this to configure your shell:
# C:\Users\xxx\workspace\programs\bin\assume-role.exe eo | Invoke-Expression

However, if I unset those environment variables, assume-role works properly and asks for my MFA and then gives me new environment variables.

[veqryn]

I think I figured out the reason right after posting this. I'll make a PR...