Silence compiler warnings

> warning: initializer 'init(configuration:)' nearly matches defaulted requirement 'init(configuration:)' of protocol 'Rule'
> note: candidate has non-matching type '(configuration: SeverityLevelsConfiguration)'
> note: move 'init(configuration:)' to an extension to silence this warning
> SwiftLintFramework.Rule:5:12: note: requirement 'init(configuration:)' declared here
>    public init(configuration: Any) throws

Tests/SwiftLintFrameworkTests/RuleTests.swift

@@ -19,6 +19,12 @@ struct RuleWithLevelsMock: ConfigurationProviderRule {
                                              kind: .style,
                                              deprecatedAliases: ["mock"])
 
+    init() {}
+    init(configuration: Any) throws {
+        self.init()
+        try self.configuration.apply(configuration: configuration)
+    }
+
     func validate(file: File) -> [StyleViolation] { return [] }
 }
 
@@ -56,6 +62,12 @@ class RuleTests: XCTestCase {
                                                  name: "",
                                                  description: "", kind: .style)
 
+        init() {}
+        init(configuration: Any) throws {
+            self.init()
+            try self.configuration.apply(configuration: configuration)
+        }
+
         func validate(file: File) -> [StyleViolation] { return [] }
     }