shellz: Set GO111MODULE=auto for Go 1.16 (#71684)
shellz: Set GO111MODULE=auto for Go 1.16 (#71684)

* shellz: Set GO111MODULE=auto for Go 1.16

This will allow this package to build with Go 1.16.

Epic: #47627

* shellz: Update license for SPDX

Per `brew audit --strict shellz`:

```
shellz:
  * Formula shellz contains deprecated SPDX licenses: ["GPL-3.0"].
    You may need to add `-only` or `-or-later` for GNU licenses (e.g. `GPL`, `LGPL`, `AGPL`, `GFDL`).
    For a list of valid licenses check: https://spdx.org/licenses/
```

Looking at https://github.com/evilsocket/shellz/blob/master/LICENSE.md,
the project is GPL 3 only, so set formula license to `GPL-3.0-only`.
stgraber/homebrew-core,sjackman/homebrew-core,Homebrew/homebrew-core,stgraber/homebrew-core,chrisfinazzo/homebrew-core,mbcoguno/homebrew-core,uyjulian/homebrew-core,filcab/homebrew-core,mbcoguno/homebrew-core,filcab/homebrew-core,lemzwerg/homebrew-core,nbari/homebrew-core,adam-moss/homebrew-core,Moisan/homebrew-core,spaam/homebrew-core,Homebrew/homebrew-core,makigumo/homebrew-core,spaam/homebrew-core,mfikes/homebrew-core,sjackman/homebrew-core,adam-moss/homebrew-core,lemzwerg/homebrew-core,nandub/homebrew-core,mfikes/homebrew-core,cblecker/homebrew-core,Linuxbrew/homebrew-core,JCount/homebrew-core,JCount/homebrew-core,nandub/homebrew-core,nbari/homebrew-core,uyjulian/homebrew-core,zyedidia/homebrew-core,chrisfinazzo/homebrew-core,makigumo/homebrew-core,Linuxbrew/homebrew-core,Moisan/homebrew-core,mbcoguno/homebrew-core,zyedidia/homebrew-core,cblecker/homebrew-core