v2.0.0

• Removed: support for stylelint versions less than 13.
• Removed: support for node@8.
• Removed: settings not related to plugin testing.
• Changed: testRule signature to only accept schema as argument.
• Added: warnings to reject schema property.
• Added: plugins schema property.
• Added: only schema property.
• Added: skip schema property.
• Fixed: TypeError: stylelint is not a function.