info: Fix style: Use a guard clause

Fix the style error:
Library/Homebrew/cmd/info.rb:88:7: C:
Use a guard clause instead of wrapping the code inside a conditional expression.

Library/Homebrew/cmd/info.rb

@@ -85,11 +85,8 @@ module Homebrew
   def info
     info_args.parse
     if args.json
-      if args.json == "v1" || args.json == true
+      raise UsageError, "invalid JSON version: #{args.json}" unless ["v1", true].include? args.json
       print_json
-      else
-        raise UsageError, "invalid JSON version: #{args.json}"
-      end
     elsif args.github?
       exec_browser(*ARGV.formulae.map { |f| github_info(f) })
     else