[JavaScript] 2.4.9 removes @ and : characters from model field names

Description

Model fields which have names containing @ or : lose those characters (e.g. @id becomes id).

For an example of the regression in the generated code, see e.g.:
https://github.com/LD4P/sinopia_server/pull/117/files#diff-7a74aae6e7d7c150c0733f6507271ee8L51

the client code with the regression was generated using the following command:

java -jar swagger-codegen-cli-2.4.9.jar generate -i swagger.yaml -l javascript --additional-properties usePromises=true -o sinopia_client/

per https://github.com/LD4P/sinopia_server#re-generating-the-sinopia-server-javascript-client-with-swagger-codegen-cli

Swagger-codegen version

2.4.9 introduces a regression compared to 2.4.8 (the replaced code in above linked diff was generated by version 2.4.2, but i confirmed in https://github.com/LD4P/sinopia_server/pull/119 that 2.4.8 still produces the desired client output)

Swagger declaration file content or url

https://github.com/LD4P/sinopia_server/blob/master/swagger.yaml#L1152-L1156

Command line used for generation

java -jar swagger-codegen-cli-2.4.9.jar generate -i swagger.yaml -l javascript --additional-properties usePromises=true -o sinopia_client/

Steps to reproduce

use the aforementioned command line invocation on the linked swagger spec. note that the generated model code does not use the specified field names.

Related issues/PRs

Suggest a fix/enhancement

revert to the behavior seen in version 2.4.8 and prior

Run the documented Java command with the linked swagger.yaml and compare the generated JavaScript model fields between versions 2.4.8 and 2.4.9. Trace where the generator transforms field names, then verify that names containing @ and : are preserved as in the earlier output.