Hello maintainer 👋 @looterz

The dockerfile used by the current project needs to be used with the built binary.

If we wanted to use containers for multi-architecture builds, it would get complicated.

So I tried submitting a PR and building the program entirely inside the container.

In addition, I also use UPX to compress the program. Compared with the past, the image size of grimd will be reduced by nearly 40%, and the running and distribution speed will also become faster.

                       Ultimate Packer for eXecutables
                          Copyright (C) 1996 - 2020
UPX 3.96        Markus Oberhumer, Laszlo Molnar & John Reiser   Jan 23rd 2020

        File size         Ratio      Format      Name
   --------------------   ------   -----------   -----------
   8503296 ->   3253452   38.26%   linux/amd64   grimd.minify

Packed 1 file.

Please review the code, if you have any questions, welcome to discuss in the issue, looking forward to your opinion

#95