Fix unknown typo in docs/tests

Author: backslash-f

README.md

@@ -76,7 +76,7 @@ case .mac(isCatalyst: true):
     // Do Catalyst stuff
 case .watch:
     // Do Watch stuff
-case .unknow:
+case .unknown:
     // Do Unknown stuff
 }
 ```

Tests/DeviceTests/DeviceTests.swift

@@ -10,7 +10,7 @@ import XCTest
     func testRetrieveDeviceType() {
         let device = Device()
         switch device.type() {
-        case .mac(isCatalyst: false), .unknow:
+        case .mac(isCatalyst: false), .unknown:
             XCTAssert(true)
         default:
             XCTFail("Expected OS to be \"Mac\" (not Catalyst) or \"Unknown\"")