Fix potential vulnerability

Author: pataar

package.json

@@ -21,7 +21,7 @@
   "dependencies": {
     "chalk": "^2.4.1",
     "debug": "^3.1.0",
-    "event-stream": "^3.3.4",
+    "event-stream": "3.3.4",
     "fancy-log": "^1.3.2",
     "lodash.assign": "^4.2.0",
     "tiny-lr": "^1.1.1",