Update Guzzle to version 5 to avoid PHP 7 issues

Author: javiereguiluz

composer.json

@@ -14,8 +14,7 @@
     },
     "require": {
         "php": ">=5.4.0",
-        "guzzlehttp/guzzle": "~4.0",
-        "guzzlehttp/progress-subscriber": "~1.1",
+        "guzzlehttp/guzzle": "~5.0",
         "symfony/console": "~2.5",
         "symfony/filesystem": "~2.5",
         "raulfraile/distill": "~0.9,!=0.9.3,!=0.9.4"