use travis cache for composer and fast finish

.travis.yml

@@ -2,25 +2,27 @@ language: php
 
 sudo: false
 
+cache:
+    directories:
+        - vendor
+        - $HOME/.composer/cache
+
 php:
     - 5.2
     - 5.3
     - 5.4
     - 5.5
     - 5.6
+    - 7.0
     - hhvm
-    - nightly
 
 env:
     - TWIG_EXT=no
     - TWIG_EXT=yes
 
-before_install:
-    - if [ ${TRAVIS_PHP_VERSION:0:3} != "5.2" ]; then composer self-update; fi
-
 install:
     # Composer is not available on PHP 5.2
-    - if [ ${TRAVIS_PHP_VERSION:0:3} != "5.2" ]; then travis_retry composer install --prefer-source; fi
+    - if [ ${TRAVIS_PHP_VERSION:0:3} != "5.2" ]; then travis_retry composer install; fi
 
 before_script:
     - if [ "$TWIG_EXT" == "yes" ]; then sh -c "cd ext/twig && phpize && ./configure --enable-twig && make && make install"; fi
@@ -28,9 +30,10 @@ before_script:
     - if [ ${TRAVIS_PHP_VERSION:0:3} == "5.2" ]; then sed -i.bak "s|vendor/autoload.php|test/bootstrap.php|" phpunit.xml.dist; fi
 
 matrix:
+    fast_finish: true
     exclude:
         - php: hhvm
           env: TWIG_EXT=yes
     allow_failures:
-        - php: nightly
+        - php: 7.0
           env: TWIG_EXT=yes