Excludes falsy values from request options

[sPaCeMoNk3yIam]

https://github.com/yarax/swagger-to-graphql/blob/master/src/getRequestOptions.ts#L54 A value should be allowed to be null, false or 0 and if set not throw an error. Here the only valid check and throw should be for undefined.

https://github.com/yarax/swagger-to-graphql/blob/master/src/getRequestOptions.ts#L58 A value should be allowed to be null, false or 0 and be passed as param. Here only undefined should not be passed.