Fix deprecation comment for Command.SetOutput (spf13#2172)

Deprecation comments should be at the start of a paragraph [1], and because
of that have a whitespace above them [2];

> To signal that an identifier should not be used, add a paragraph to its
> doc comment that begins with Deprecated: followed by some information
> about the deprecation (...)

With the whitespace missing, some tools, including pkg.go.dev [3] don't
detect it to be deprecated.

[1]: https://go.dev/wiki/Deprecated
[2]: https://go.dev/doc/comment#paragraphs
[3]: https://pkg.go.dev/github.com/spf13/[email protected]#Command.SetOutput

Signed-off-by: Sebastiaan van Stijn <[email protected]>

command.go

@@ -281,6 +281,7 @@ func (c *Command) SetArgs(a []string) {
 
 // SetOutput sets the destination for usage and error messages.
 // If output is nil, os.Stderr is used.
+//
 // Deprecated: Use SetOut and/or SetErr instead
 func (c *Command) SetOutput(output io.Writer) {
 	c.outWriter = output