Fix travis CI script to update SwiftPM dependency

Author: dreampiggy

.travis.yml

@@ -33,4 +33,5 @@ script:
   - pod install --project-directory=Example
   - xcodebuild build -workspace Example/SDWebImageSwiftUI.xcworkspace -scheme SDWebImageSwiftUIDemo -sdk iphonesimulator -destination 'name=iPhone 8' ONLY_ACTIVE_ARCH=NO | xcpretty -c
 
+  - swift package update
   - swift build

Package.swift

@@ -33,7 +33,6 @@ let package = Package(
             name: "SDWebImageSwiftUIObjC",
             dependencies: ["SDWebImage"],
             path: "SDWebImageSwiftUI/Classes/ObjC",
-            sources: ["SDAnimatedImageInterface.h", "SDAnimatedImageInterface.m"],
             publicHeadersPath: "."
         )
     ]