[BUG] openapi-generator-maven-plugin generates incorrect package import for go-server

[jixuan1989]

Description

When using openapi-generator-maven-plugin to generate go-server codes, there are two errors in the generated codes:
(openapi-generator-version is 5.0.0)

1. "mime/multipart" is forget to import in router.go

2. `github.com/gorilla/mux` should not be imported in `api_default.go` file.
   

How to produce:

I can stable reproduce it using the following file:

1. get codes from: https://github.com/apache/iotdb/tree/openapi/openapi
2. run mvn generate-codes
3. the generated source is under target/generated-sources/go

see the codes and error tips by GoLand.

[jherbage]

Also affected by this and I am using the docker image openapitools/openapi-generator-cli

[ys]

Same here, a simple fix would be this master...ys:patch-1