MFA problem with v4.2.0

[pbyrne]

When I try to run audit with v4.2.0 using my account credentials (and MFA), it stalls and eventually fails. When I roll back to v4.1.0, without any changes to my configuration, it works.

$ sport-ngin-aws-auditor --version     
sport-ngin-aws-auditor version 4.2.0

$ sport-ngin-aws-auditor audit dribbble
Authenticating with AWS using credentials file.
Enter MFA token: [SNIP]
Sorry, something seems to have gone wrong.
error: unable to sign request without credentials set

$ sport-ngin-aws-auditor --version     
sport-ngin-aws-auditor version 4.1.0

$ sport-ngin-aws-auditor audit dribbble      
Enter MFA token: [SNIP]
AWS AUDIT FOR dribbble
… and the report follows