Create a typealias for SnapshotTestCase when not on Linux (#169)

* Create a typealias for SnapshotTestCase when not on Linux

* Deprecate SnapshotTestCase typealias on swift 5

* Added renamed to the SnapshotTestCase typealias

Author: f-meloni

Sources/SnapshotTesting/SnapshotTestCase.swift

@@ -1,6 +1,10 @@
-#if os(Linux)
 import XCTest
 
+#if !os(Linux)
+@available(swift, obsoleted: 5.0, renamed: "XCTestCase", message: "Please use XCTestCase instead")
+public typealias SnapshotTestCase = XCTestCase
+#else
+
 /// An XCTest subclass that provides snaphot testing helpers.
 open class SnapshotTestCase: XCTestCase {
   /// Whether or not to record all new references.

Tests/SnapshotTestingTests/SnapshotTestingTests.swift

@@ -9,13 +9,7 @@ import SpriteKit
 import WebKit
 #endif
 
-#if os(Linux)
-typealias TestCase = SnapshotTestCase
-#else
-typealias TestCase = XCTestCase
-#endif
-
-class SnapshotTestingTests: TestCase {
+final class SnapshotTestingTests: SnapshotTestCase {
   override func setUp() {
     super.setUp()
     diffTool = "ksdiff"