provisoner/salt-masterless: lowercase package name

/cc @rgarcia - I don't know of any Go packages that follow this naming
convention so I just lowercased it.

provisioner/salt-masterless/provisioner.go

 // This package implements a provisioner for Packer that executes a
 // saltstack highstate within the remote machine
-package saltMasterless
+package saltmasterless
 
 import (
 	"errors"

provisioner/salt-masterless/provisioner_test.go

-package saltMasterless
+package saltmasterless
 
 import (
 	"github.com/mitchellh/packer/packer"