Merge pull request #284 from elifesciences/widen-symfony-serialiser-support

Widen support for symfony/serializer up to 5.x

Author: scottaubrey

composer.json

@@ -20,7 +20,7 @@
         "elife/api-client": "^1.0",
         "guzzlehttp/promises": "^1.0",
         "guzzlehttp/psr7": "^1.0",
-        "symfony/serializer": "^2.8.2 || ^3.0.2"
+        "symfony/serializer": "^2.8.2 || ^3.0.2 || ^4.0 || ^5.0"
     },
     "require-dev": {
         "csa/guzzle-cache-middleware": "^1.0",