Update macOS advanced install with homebrew

osgeo/osgeo4mac is no longer maintained, proj, geos, and gdal can be installed straight from the homebrew repository.

learners/setup.md

@@ -23,11 +23,11 @@
 
 | Software | Install | Manual | Available for         | Description                                                   | 
 | -------- | ------- | ------ | --------------------- | ------------------------------------------------------------- |
 | [GDAL](https://www.gdal.org)         | [Link](https://gdal.org/download.html)        | [Link](https://gdal.org)       | Linux, MacOS, Windows | Geospatial model for reading and writing a variety of formats | 
 | [GEOS](https://trac.osgeo.org/geos)         | [Link](https://trac.osgeo.org/geos)        | [Link](https://geos.osgeo.org/doxygen/)       | Linux, MacOS, Windows | Geometry models and operations                                | 
 | [PROJ.4](https://proj4.org)         | [Link](https://proj4.org/install.html)        | [Link](https://proj4.org/index.html)       | Linux, MacOS, Windows | Coordinate reference system transformations                   | 
 | [R](https://www.r-project.org)         | [Link](https://cloud.r-project.org)        | [Link](https://cloud.r-project.org)       | Linux, MacOS, Windows | Software environment for statistical and scientific computing | 
 | [RStudio](https://www.rstudio.com)         | [Link](https://www.rstudio.com/products/rstudio/download/#download)        |        | Linux, MacOS, Windows | GUI for R                                                     | 
 | [UDUNITS](https://www.unidata.ucar.edu/software/udunits/)         | [Link](https://www.unidata.ucar.edu/downloads/udunits/index.jsp)        | [Link](https://www.unidata.ucar.edu/software/udunits/#documentation)       | Linux, MacOS, Windows | Unit conversions                                              | 
 
 We provide quick instructions below for installing the various software needed for this workshop. At points, they assume familiarity with the command line and with installation in general. As there are different operating systems and many different versions of operating systems and environments, these may not work on your computer. If an installation doesn't work for you, please refer to the installation instructions for that software listed in the table above.
@@ -61,10 +61,9 @@
 Alternatively, participants who are comfortable with the command line can install the geospatial libraries individually using [homebrew](https://brew.sh):
 
 ```bash
-$ brew tap osgeo/osgeo4mac && brew tap --repair
 $ brew install proj
 $ brew install geos
-$ brew install gdal2
+$ brew install gdal
 ```
 
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