Install instructions for Ubuntu/Linux use brew when they should use apt

[jimoquinn]

It is my opinion that dependencies should be very easy to install so developers spend their time writing code with IOST, not wrestling with the development environment.

The Ubuntu/Linux instructions for installing "git lfs" use brew, which may be fine, but apt is used throughout the install instructions for Ubuntu/Linux and brew is not. Here is the location: https://github.com/iost-official/iost-docs/blob/master/docs/4-running-iost-node/Environment-Configuration.md

Also, apt is native to the OS and brew is not.