vpm: outdated command (#5833)

cmd/v/help/default.txt

@@ -31,6 +31,7 @@ V supports the following commands:
    remove            Remove a module that was installed from VPM.
    search            Search for a module from VPM.
    update            Update an installed module from VPM.
+   outdated          List installed modules that need updates.
 * Others:
    build             Build a V code in the provided path (the default, so you can skip the word `build`).
    translate         Translate C code to V (coming soon in 0.3).

cmd/v/v.v

@@ -70,7 +70,7 @@ fn main() {
 			println('Translating C to V will be available in V 0.3')
 			return
 		}
-		'search', 'install', 'update', 'remove' {
+		'search', 'install', 'update', 'outdated', 'remove' {
 			util.launch_tool(prefs.is_verbose, 'vpm', os.args[1..])
 			return
 		}