Disabled opt-in rule warning violates json contract

[rounak]

New Issue Checklist

• Updated SwiftLint to the latest version
• I searched for existing GitHub issues

Describe the bug

Using the json reporter when linting prints output that's not json.

command: ./Pods/SwiftLint/swiftlint lint --reporter json --quiet

output:

Found a configuration for 'modifier_order' rule, but it is disabled on 'disabled_rules'.
[
    {

The warning introduced with #1350 breaks the output from following the standard json schema.

Complete output when running SwiftLint, including the stack trace and command used

$ ./Pods/SwiftLint/swiftlint lint --reporter json --quiet

Environment

• SwiftLint version (run swiftlint version to be sure)? 0.33.1
• Installation method used (Homebrew, CocoaPods, building from source, etc)? Cocoapods
• Which Xcode version are you using (check xcode-select -p)? 10.1.0

[marcelofabri]

That message should be printed to stderr, while the json should be printed to stdout. You can append 2>/dev/null to omit the stderr output.

[rounak]

Thank you!