upgrade packr2, go version to 1.16, and bluemonday 1.0.15

[sio4]

Please review this PR:

• using packr2
• updated go version to 1.16
• upgraded bluemonday version from 1.0.2 to 1.0.15 which is safer.

[sio4]

additionally, this will obsolete #3.

[sio4]

From my quick research, it seems like the origin of the inclusion of the old version of bluemonday (which is 1.0.2) is on this package. This PR will help the other packages. I think gobuffalo/plush#146 is also related.

[paganotoni]

Thanks sio4!

[sio4]

Thanks @paganotoni! once it is included in the next release, maybe v1.1.1 or v1.2.0, I will check other packages for it. currently, I found helpers use it directly, and some other packages genny, fizz, cli, and release indirectly depend on it.