[Nim] bugfix for the case when path contains multiple parameters

Created by: darklynx

If REST end-point has a path with multiple parameters current api.mustache generates a broken Nim-code by repeating path string multiple times, for example:

proc getCompanyUser*(httpClient: HttpClient, companyId: string, userId: string): (Option[User], Response) =
  ## Get user of a company

  let response = httpClient.get(basepath & fmt"/companies/{companyId}/users/{userId}"fmt"/companies/{companyId}/users/{userId}")
  constructResult[User](response)

after this fix is applied the result will be as is was designed by original author:

proc getCompanyUser*(httpClient: HttpClient, companyId: string, userId: string): (Option[User], Response) =
  ## Get user of a company

  let response = httpClient.get(basepath & fmt"/companies/{companyId}/users/{userId}")
  constructResult[User](response)

Note: unfortunately Petstore example does not contain any API paths with 2 or more path parameters, otherwise the issue could have been caught before.

Note 2: unfortunately Nim language has no members in Technical Committee

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