Drop support for io.js, fix minor issue with node extension
diff --git a/package.json b/package.json
index 2228884..588425d 100644
--- a/package.json
+++ b/package.json
@@ -52,7 +52,7 @@
     "poisson-process": "^0.2.1"
   },
   "engines": {
-    "node": ">=1.1.0"
+    "node": ">=4"
   },
   "binary": {
     "module_name": "grpc_node",