Use reggen instead of faker.Regexify

[exgphe]

reggen generates string by regex of a better quality.
Take a regex of IPv4 for example.

faker.Regexify("^(([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])\\.){3}([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])(%[\\p{N}\\p{L}]+)?$")

could produce "(8\.)))62"

while

reggen.Generate("^(([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])\\.){3}([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])(%[\\p{N}\\p{L}]+)?$", 15)

produces "72.65.44.117".

[strider2038]

@exgphe Hello! Thank you for the pull request. There are some failing tests. Can you fix it?

https://scrutinizer-ci.com/g/muonsoft/openapi-mock/inspections/6bf14f63-82ff-43b9-ac70-56262fffbfaa

[exgphe]

According to OAI/OpenAPI-Specification#1985 the pattern field should not include the wrapping slashes, so I modified the test function.