points2grid: update to 1.3.0

This pull request updates points2grid to 1.3.0. 1.3.0 added GDAL output support (GeoTIFF only) for the `points2grid` command-line utility. 
@hobu For your [reference](https://github.com/Homebrew/homebrew/blob/master/Library/Homebrew/formula.rb#L321-L337).