test against different dependency versions

* by default, run with latest stable versions
* add a job with lowest stable constrained deps
* run with upcoming releases of required deps

Author: xabbuh

.travis.yml

@@ -10,8 +10,15 @@ php:
   - 7.1
   - hhvm
 
+env:
+  - COMPOSER_OPTIONS="--prefer-stable"
+
 matrix:
   include:
+    - php: 7.0
+      env: COMPOSER_OPTIONS="--prefer-lowest --prefer-stable"
+    - php: 7.0
+      env: COMPOSER_OPTIONS=""
     - php: 7.1
       env: TEST_COVERAGE=true
   allow_failures:
@@ -26,7 +33,7 @@ before_install:
   - composer self-update
   - if [[ $TEST_COVERAGE ]]; then PHPUNIT_FLAGS="--coverage-clover clover.xml"; fi
 
-install: travis_retry composer install --no-interaction --prefer-dist
+install: travis_retry composer update --no-interaction --prefer-dist $COMPOSER_OPTIONS
 
 script:
   - vendor/bin/phpunit -v $PHPUNIT_FLAGS

composer.json

@@ -20,6 +20,7 @@
         "friendsofphp/php-cs-fixer": "^1.8.0",
         "phpunit/phpunit": "^4.6.6"
     },
+    "minimum-stability": "dev",
     "autoload": {
         "psr-0" : {
             "Sentry\\SentryBundle\\": "src/"