bug #182 Update Guzzle to version 5 to avoid PHP 7 issues (javiereguiluz)

This PR was squashed before being merged into the 1.0-dev branch (closes #182).

Discussion
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Update Guzzle to version 5 to avoid PHP 7 issues

`guzzlehttp/progress-subscriber` has been removed because it's declared as `DEPRECATED` and it requires Guzzle 4.

Commits
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815b067 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"