Currently due to the occurrence of 6 arguments from
`gen-ldflags.go` leads to a bug where the binaries
genenerated have wrong names.
As shown below.
```
If you want to build for all, Just press Enter: linux/amd64
--> linux/amd64:github.com/minio/minio
$ ls release/linux-amd64/
[2017-05-04 23:08:51 PDT] 17MiB minio
[2017-05-04 23:08:51 PDT] 17MiB minio.2017-05-05T06:08:22Z
[2017-05-04 23:08:51 PDT] 76B minio.shasum
```
This PR fixes this issue by retaining the previous release
binary names.
```
If you want to build for all, Just press Enter: linux/amd64
--> linux/amd64:github.com/minio/minio
$ ls release/linux-amd64/
[2017-05-04 23:08:51 PDT] 17MiB minio
[2017-05-04 23:08:51 PDT] 17MiB minio.RELEASE.2017-05-05T06-08-22Z
[2017-05-04 23:08:51 PDT] 76B minio.shasum
```
