testTarget method's description of parameter path (swiftlang#2906)

the description of parameter path is not right

Author: hellomsg

Documentation/PackageDescription.md

@@ -523,7 +523,7 @@ public static func target(
 /// - Parameters:
 ///   - name: The name of the target.
 ///   - dependencies: The dependencies of the target. These can either be other targets in the package or products from other packages.
-///   - path: The custom path for the target. By default, targets will be looked up in the <package-root>/Sources/<target-name> directory.
+///   - path: The custom path for the target. By default, targets will be looked up in the <package-root>/Tests/<target-name> directory.
 ///       Do not escape the package root, i.e. values like "../Foo" or "/Foo" are invalid.
 ///   - exclude: A list of paths to exclude from being considered source files. This path is relative to the target's directory.
 ///   - sources: An explicit list of source files.