Fix travis run by updating ffmpeg

Update .travis.yml

There is no ppa for precise (ubuntu 12.04) to use ffmpeg 3. So I updated
travis to run trusty (ubuntu 14.04) but it can't test on php5.3 in that
configuration. That's why I drop the test support for php 5.3.

Drop php 5.3 support

.travis.yml

@@ -1,31 +1,34 @@
 language: php
 
+dist: trusty
+
 branches:
   only:
     - master
 
 php:
-  - 5.3
   - 5.4
   - 5.5
   - 5.6
   - 7.0
+  - 7.1
   - hhvm
 
 matrix:
   allow_failures:
     - php: hhvm
   include:
-    - php: 5.3
+    - php: 5.4
       env: COMPOSER_FLAGS="--prefer-lowest"
 
 before_install:
-  - sudo apt-get update
+  - sudo add-apt-repository ppa:mc3man/trusty-media -y
+  - sudo apt-get update -q
   - composer self-update
   - if [ "$COMPOSER_FLAGS" == "--prefer-lowest" ]; then composer require "roave/security-advisories" dev-master --no-update; fi;
 
 install:
-  - sudo apt-get install -y ffmpeg libavcodec-extra-53
+  - sudo apt-get install -y ffmpeg
   - composer update --prefer-source $COMPOSER_FLAGS
 
 script: