Fixed some folders not getting created on fresh installs, throwing a few errors

lib/npmPostinstall.js

@@ -0,0 +1,18 @@
+var mkdirp = require("mkdirp");
+
+var directories = [
+	"database/linvodb",
+	"sharedMods",
+	"instances",
+];
+
+directories.forEach(path => {
+	mkdirp("database/linvodb", function(err){
+		if(err){
+			console.error("Unable to mkdirp "+path);
+			console.error(err);
+		} else {
+			console.log("mkdirp "+path);
+		}
+	});
+})