fix(build): make assembly definitions compatible to unity 2018 and 2019

Author: mamoonraja

Tests/IBM.Watson.Tests.asmdef

@@ -1,17 +1,21 @@
 {
     "name": "IBM.Watson.Tests",
-  "references": [
-    "WatsonUnitySDK",
-    "IBM.Cloud.SDK"
-  ],
+    "references": [
+        "WatsonUnitySDK",
+        "IBM.Cloud.SDK"
+    ],
     "optionalUnityReferences": [
         "TestAssemblies"
     ],
     "includePlatforms": [],
     "excludePlatforms": [],
     "allowUnsafeCode": false,
-    "overrideReferences": false,
-    "precompiledReferences": [],
-    "autoReferenced": true,
-    "defineConstraints": []
+    "overrideReferences": true,
+    "precompiledReferences": [
+        "nunit.framework.dll",
+        "Newtonsoft.Json.dll"
+    ],
+    "autoReferenced": false,
+    "defineConstraints": [],
+    "versionDefines": []
 }