command/providers: Enable processing of meta-parameters

This will enable proper colouring of the output, like for other commands.

command/providers.go

@@ -24,6 +24,7 @@ func (c *ProvidersCommand) Synopsis() string {
 }
 
 func (c *ProvidersCommand) Run(args []string) int {
+	c.Meta.process(args, false)
 
 	cmdFlags := c.Meta.flagSet("providers")
 	cmdFlags.Usage = func() { c.Ui.Error(c.Help()) }