beforeBuildCommand doesn't run in a shell

[gabcoh]

Describe the bug
The beforeBuildCommand key in src-tauri/tauri.conf.json is not run in a shell. It is split by spaces and then the first word becomes the command and the rest are the arguments. Quoting is not respected and you can not run commands like cd dir && command. As of 164e3a4 beforeDevCommand is run in a shell, but it seems like in dev both beforeBuildCommand and beforeDevCommand are run by splitting on spaces.

To Reproduce
Steps to reproduce the behavior:

1. Create a new project
2. set beforeBuildCommand in src-tauri/tauri.conf.json to echo A && echo B
3. run yarn tauri build
4. A && echo B is printed
   Expected behavior
   This should be printed

A
B

Screenshots
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Platform and Versions (please complete the following information):

OS: linux
Node: 15.8.0
NPM: 6.14.11
Yarn: 1.22.10
Rustc: 1.50.0

Additional context
Add any other context about the problem here.

Stack Trace

[gabcoh]

This seems like a pretty easy fix. At least on Mac and Linux you could just run the command through sh -c, but I'm not sure what the equivalent is for windows.