update demo name 😅

Author: sunlubo

Package.swift

@@ -12,7 +12,7 @@ let package = Package(
         ),
         .executable(
             name: "SwiftSDL2Demo",
-            targets: ["Demo"]
+            targets: ["SwiftSDL2Demo"]
         )
     ],
     dependencies: [
@@ -23,8 +23,9 @@ let package = Package(
             name: "SwiftSDL2"
         ),
         .target(
-            name: "Demo",
-            dependencies: ["SwiftSDL2"]
+            name: "SwiftSDL2Demo",
+            dependencies: ["SwiftSDL2"],
+            path: "Sources/Demo"
         ),
         .testTarget(
             name: "SwiftSDL2Tests",