fix: allow netresearch/jsonmapper 2.0 (#39)

Author: a-menshchikov

composer.json

@@ -21,7 +21,7 @@
     },
     "require": {
         "php": ">=7.0",
-        "netresearch/jsonmapper": "^1.0",
+        "netresearch/jsonmapper": "^1.0 || ^2.0",
         "phpdocumentor/reflection-docblock": "^4.0.0 || ^5.0.0"
     },
     "require-dev": {