Update travis config.

.travis.yml

@@ -1,17 +1,37 @@
 language: php
 
+sudo: false
+
+dist: trusty
+
 php:
  - '7.0'
+ - '7.1'
+
+env:
+  global:
+    - DEFAULT=1
+
+matrix:
+  fast_finish: true
+
+  include:
+    - php: '7.0'
+      env: PHPCS=1 DEFAULT=0
 
 cache:
   directories:
    - vendor
 
 install:
- - composer install
+ - composer install --prefer-dist
 
 script:
- - vendor/bin/phpunit --coverage-clover=coverage.xml
+ - if [[ $DEFAULT = 1 && $TRAVIS_PHP_VERSION == 7.0 ]]; then vendor/bin/phpunit --coverage-clover=coverage.xml; fi
+
+ - if [[ $DEFAULT = 1 && $TRAVIS_PHP_VERSION != 7.0 ]]; then vendor/bin/phpunit; fi
+
+ - if [[ $PHPCS = 1 ]]; then vendor/bin/phpcs -p --extensions=php --standard=PSR2 ./src ./tests; fi
 
 after_success:
- - bash <(curl -s https://codecov.io/bash)
+ - if [[ $DEFAULT = 1 && $TRAVIS_PHP_VERSION = 7.0 ]]; then bash <(curl -s https://codecov.io/bash); fi