Add "ext-imap" to composer.json

This library needs it. :)

Author: asm89

composer.json

@@ -12,7 +12,8 @@
     }
   ],
   "require": {
-    "php": ">=5.3.0"
+    "php": ">=5.3.0",
+    "ext-imap": "*"
   },
   "autoload": {
     "psr-0": {"Fetch": "src/"}