Update version specifications for Wasmer (#482)

Added missing Wasmer version specifications for reference types,
threads, and exceptions.

Author: syrusakbary

features.json

@@ -477,6 +477,9 @@
         "esmIntegration": null,
         "jspi": null,
         "jsStringBuiltins": null,
+        "referenceTypes": "2.0.0",
+        "threads": "4.0.0",
+        "exceptionsFinal": "6.0.0",
         "multiValue": "1.0",
         "mutableGlobals": "0.7",
         "referenceTypes": "2.0",