chore: method stubs

Author: saitho

packages.go

@@ -10,7 +10,8 @@ type Package struct {
 	Vendor PackageVendor
 }
 
-func InstallPackage(packages []Package) {
+func InstallPackage(packages []Package) error {
 	// mock function
 	// behaviour is implemented in StackHead main repository
+	return nil
 }

stackhead.go

@@ -1,6 +1,7 @@
 package pluginlib
 
-func StackHeadExecute(command string, args interface{}) {
+func StackHeadExecute(command string) error {
 	// mock function
 	// behaviour is implemented in StackHead main repository
+	return nil
 }