packer: -machine-readable not double hyphen

command/build/help.go

@@ -10,6 +10,7 @@ Options:
 
   -debug                     Debug mode enabled for builds
   -force                     Force a build to continue if artifacts exist, deletes existing artifacts
+  -machine-readable          Machine-readable output
   -except=foo,bar,baz        Build all builds other than these
   -only=foo,bar,baz          Only build the given builds by name
   -var 'key=value'           Variable for templates, can be used multiple times.

packer.go

@@ -122,7 +122,7 @@ func main() {
 // to remove this flag.
 func extractMachineReadable(args []string) ([]string, bool) {
 	for i, arg := range args {
-		if arg == "--machine-readable" {
+		if arg == "-machine-readable" {
 			// We found it. Slice it out.
 			result := make([]string, len(args)-1)
 			copy(result, args[:i])

packer/environment.go

@@ -301,7 +301,7 @@ func (e *coreEnvironment) printHelp() {
 	}
 
 	e.ui.Say("\nGlobally recognized options:")
-	e.ui.Say("    --machine-readable    Machine-readable output format.")
+	e.ui.Say("    -machine-readable    Machine-readable output format.")
 }
 
 // Returns the UI for the environment. The UI is the interface that should