vstplugin build script ammendments

[mccrmck]

As per this thread:

To install the VST2 and VST3 SDKs, lines 25-30 of vstplugin.sh should instead be:

cd ./vstplugin

# Get VST2
./.git-ci/get_vst2.sh

# Get VST3
./.git-ci/get_vst3.sh

cd ..

Also:

Line 33 in vstplugin.sh seems to be missing -DCMAKE_OSX_ARCHITECTURES="$OSX_ARCH"

[madskjeldgaard]

Nice, thanks! Feel free to make a pull request

[mccrmck]

Sorry, was on holiday last week...done now!