use lower scssphp version for php 5.3 compatibility

the functionality we are using is present

.travis.yml

@@ -23,8 +23,6 @@ cache:
     - vendor
 
 install:
-  # set low version, so deps can be installed on 5.3
-  - composer config platform.php 5.4
   - composer update --no-interaction --prefer-source
 
 script:

composer.json

@@ -34,7 +34,7 @@
 	},
 	"require-dev": {
 		"leafo/lessphp": "~0.4.0",
-		"leafo/scssphp": "^0.6.6",
+		"leafo/scssphp": "^0.3.0",
 		"meenie/javascript-packer": "~1.1",
 		"phpunit/phpunit": "4.8.*",
 		"tedivm/jshrink": "~1.1.0"