add instantiate step (#72)

Author: findmyway

.github/workflows/ExportPluto.yaml

@@ -33,7 +33,8 @@ jobs:
 
             - name: Run & export Pluto notebooks
               run: julia -e 'using Pkg;
-                  Pkg.activate(mktempdir());
+                  Pkg.activate(".");
+                  Pkg.instantiate();
                   Pkg.add([
                     Pkg.PackageSpec(name="PlutoSliderServer", version="0.2.1-0.2"),
                   ]);