Locked ps-tree version to 1.1.1

Author: punitx

package.json

@@ -19,7 +19,7 @@
   "dependencies": {
     "https-proxy-agent": "^2.2.1",
     "is-running": "^2.0.0",
-    "ps-tree": "^1.1.0",
+    "ps-tree": "=1.1.1",
     "sinon": "^1.17.6",
     "temp-fs": "^0.9.9"
   },