Update node-environment-flags to 1.0.6 (#4118)

node-environment-flags 1.0.5 and lower do not contain a LICENSE file
which can make compliance difficult.

Author: kylef

package-lock.json

@@ -537,7 +537,7 @@
     "minimatch": "3.0.4",
     "mkdirp": "0.5.1",
     "ms": "2.1.1",
-    "node-environment-flags": "1.0.5",
+    "node-environment-flags": "1.0.6",
     "object.assign": "4.1.0",
     "strip-json-comments": "2.0.1",
     "supports-color": "6.0.0",