Version 1.5.2 incompatible with serverless >= 2.31

[cwill-evonier]

sls.yml

plugins:
  - serverless-certificate-creator

package.json

  "devDependencies": {
    "serverless-certificate-creator": "1.5.2"
}

Serverless: Deprecation warning: Plugin "CreateCertificatePlugin" attempts to extend old variables resolver. Ensure to rely on latest version of a plugin and if this warning is still displayed please report the problem at plugin issue trackerStarting with next major release, old variables resolver will not be supported.
            
            More Info: https://www.serverless.com/framework/docs/deprecations/#NEW_VARIABLES_RESOLVER

[jesusch]

see also pull #50