Update dependencies to resolve CVEs

[James Navin]

We have set up security scanning for this library, and it has identified a number of CVEs in dependencies used by the library.

We should update dependencies to move to known secure versions where possible.

[Alex Stevens]

Can the swagger-parser get updated too?:
https://bitbucket.org/atlassian/swagger-request-validator/issues/228/referencing-from-a-json-schema-v7-file

[James Navin]

Yep - I will look at bumping the parser version at the same time.

[James Navin]

Available in v2.7.0