* Fix pkcs7 parsing in some cases
brings in https://github.com/mozilla-services/pkcs7/pull/61 from upstream
In some cases but not all, aws includes a certificate in the pkcs7 response,
and currently vault fails to parse those certificates:
```
URL: PUT https://vault.example.com/v1/auth/aws/login
Code: 500. Errors
* failed to parse the BER encoded PKCS#7 signature: ber2der: Invalid BER format
```
This fixes logins on those instances. Note we could not readily ascertain why
some instances have those certificates and others don't.
* Add changelog entry
* Correct missed line
