[json] JSON is not defined

[qiaojingx]

Description

Got error Error: JSON is not defined, when running PMESaveRestore.js on Arduino 101.

Test Code

PMESaveRestore.js

Steps to Reproduction

1. make JS=samples/PMESaveRestore.js
2. make dfu

Actual Result

message Error: JSON is not defined is printed.

Expected Result

Samples should be executed successfully.

Test Builds

Branch	Commit Id	Target Device	Test Date	Result
master	78c9749	Arduino 101	Jun 20, 2017	Fail

Additional Information

[qiaojingx]

Verified with commit 1f74fb9. This issue is not reproducible.