Remove conflicts in composer.json

.travis.yml

@@ -19,7 +19,7 @@ addons:
 
 before_script:
   - pecl install -f mongodb-${DRIVER_VERSION}
-  - composer install --dev
+  - composer install
 
 script:
     - vendor/bin/phpunit

composer.json

@@ -13,9 +13,6 @@
     "require-dev": {
         "phpunit/phpunit": "^4.8 || ^5.0"
     },
-    "conflict": {
-        "ext-mongo": "*"
-    },
     "replace": {
         "ext-mongo": "self.version"
     },