Issue #28: Add zlib dependency (#29)

Author: webflo

composer.json

@@ -9,7 +9,8 @@
  "guzzlehttp/guzzle": "~6.1",
  "codegyre/robo": "^0.7.1",
  "pear/archive_tar": "~1.0",
- "ext-curl": "*"
+ "ext-curl": "*",
+ "ext-zlib": "*"
  },
  "autoload": {
  "psr-4": {