[Travis] Only reinstall packages if updated.

.travis.yml

@@ -26,8 +26,8 @@ before_install:
   - mkdir -p "${DEVKITPRO}"
   - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then wget https://github.com/devkitPro/pacman/releases/download/devkitpro-pacman-1.0.1/devkitpro-pacman.deb -O /tmp/devkitpro-pacman.deb; fi
   - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then sudo dpkg -i /tmp/devkitpro-pacman.deb; fi
-  - yes | sudo dkp-pacman -Syu devkitPPC
-  - yes | sudo dkp-pacman -Syu general-tools
+  - yes | sudo dkp-pacman -Syu devkitPPC --needed
+  - yes | sudo dkp-pacman -Syu general-tools --needed
 
 install:
   - cd $PORTLIBREPOS