Multiple API - Getting 404s when running /example/multiple

[blink-daniel]

Getting 404s when running the below example:
https://github.com/swaggo/gin-swagger/tree/master/example/multiple

Steps to reproduce:

1. run the multiple api example

gh repo clone swaggo/gin-swagger
cd gin-swagger/example/multiple
go run main.go 

2. open http://localhost:8080/swagger/v1/index.html
3. open http://localhost:8080/swagger/v2/index.html
4. open again http://localhost:8080/swagger/v1/index.html
5. the error should reproduce for instance v1 - blank page due to 404s. (instance v2 still works)

*Reproduced on macOS/Chrome on latest swag/gin-swagger master branch

[blink-daniel]

closing, duplicate of #224