Migrate from "should" to "chai"

[kg0r0]

Description

Fixed #653

I fixed it the same way as node-saml Issue. (node-saml/node-saml#41)
There are some points that have been specially dealt with.

(1) In the following code, "match" was not used. The reason I did not use "match" in the following code is because, as shown in this Issue, if the comparison target is a string, an error like "TypeError: re.exec is not a function" will occur.
https://github.com/node-saml/passport-saml/pull/687/files#diff-855cb92ef30e211592bac8169dcf23d250f18e57f7f662bab42f31136b3794eeR234

(2) The following code does not use "startWith".The reason for this is that the same does not exist in chai as described in this article.
https://github.com/node-saml/passport-saml/pull/687/files#diff-855cb92ef30e211592bac8169dcf23d250f18e57f7f662bab42f31136b3794eeR165

Please let me know if there is anything else that needs to be fixed in addition to the above, so that I can fix it as soon as possible.

Checklist:

• Issue Addressed: [x]
• Link to SAML spec: [ ]
• Tests included? [x]
• Documentation updated? [ ]