Fix warning

Author: ufechner7

test/test_installation4

@@ -10,6 +10,6 @@ cd /tmp/test
 export JULIA_DEPOT_PATH=/tmp/testdepot 
 mkdir test 
 cd test
-julia --project="." -e 'using Pkg; pkg"add KiteModels#main"'
+julia --project=. -e 'using Pkg; Pkg.add(Pkg.PackageSpec(name="KiteModels", rev="main"))'
 julia --project -e 'using KiteModels; KiteModels.install_examples()'
 julia --project -e 'using KiteModels; include("examples/ram_air_kite.jl")'