Fix link (#171)

README.md

@@ -110,7 +110,7 @@ locations below:
 |                                                       Location                                                       |
 | :------------------------------------------------------------------------------------------------------------------: |
 | [AWS IoT Device SDK for Embedded C](https://github.com/aws/aws-iot-device-sdk-embedded-C#releases-and-documentation) |
-|       [FreeRTOS.org](https://freertos.org/Documentation/api-ref/coreJSON/docs/doxygen/output/html/index.html)        |
+|       [GitHub.io](https://freertos.github.io/coreJSON/v3.3.0/)        |
 
 Note that the latest included version of the coreJSON library may differ across
 repositories.