Update travis to use cached dependencies

.travis.yml

@@ -1,12 +1,15 @@
 language: swift
 osx_image: xcode10
+cache:
+  directories:
+  - Carthage
 before_install:
   - brew update
   - brew outdated carthage || brew upgrade carthage
 before_script:
   # bootstrap the dependencies for the project
   # you can remove if you don't have dependencies
-  - carthage bootstrap
+  - carthage bootstrap --verbose --no-use-binaries --platform iOS --cache-builds
 script:
   - swiftlint 
   - xcodebuild -project BookPlayer.xcodeproj -scheme BookPlayer -destination 'platform=iOS Simulator,OS=11.3,name=iPhone 5s' test