Tweaking travis config, removing composer.lock

.gitignore

@@ -1,3 +1,4 @@
 *.json
+composer.lock
 !composer.json
 vendor

.travis.yml

@@ -1,17 +1,20 @@
 language: php
 php:
-  - '5.6'
-  - '7.0'
-  - '7.1'
+  - 5.5
+  - 5.6
+  - 7.0
+  - 7.1
+  - nightly
 matrix:
   allow_failures:
+    - php: 5.5
     - php: 5.6
+    - php: nightly
   fast_finish: true
 cache:
   directories:
     - $HOME/.composer/cache/files
 before_script:
-  - echo $TRAVIS_PHP_VERSION
   - phpenv global "$TRAVIS_PHP_VERSION"
   - composer config extra.platform.php $TRAVIS_PHP_VERSION
   - composer require php-coveralls/php-coveralls