Support CssToInlineStyles 2.2 and above (PR #34)

Fixes #25.

Author: nclsHart

composer.json

@@ -12,7 +12,7 @@
     "require" : {
         "php": ">=5.5",
         "swiftmailer/swiftmailer": "^5.1",
-        "tijsverkoyen/css-to-inline-styles": "^2.1, <2.2"
+        "tijsverkoyen/css-to-inline-styles": "^2.1"
     },
     "require-dev" : {
         "phpunit/phpunit": "^4.0|^5.0",