Fix broken links (#515)

Author: AniruddhaKanhere

README.md

@@ -228,7 +228,6 @@ 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/ota-for-aws-iot-embedded-sdk/docs/doxygen/output/html/index.html) |
 
 Note that the latest included version of coreMQTT may differ across
 repositories.

source/include/ota_config_defaults.h

@@ -66,7 +66,7 @@
  * The configuration parameter specifies the size of the stack that will be allocated
  * to the task being created (the size is specified in words, not bytes!). The amount
  * of stack required is dependent on the application specific parameters,
- * for more information [Link](https://www.freertos.org/FAQMem.html#StackSize)
+ * for more information [Link](https://www.freertos.org/Why-FreeRTOS/FAQs/Memory-usage-boot-times-context#how-big-should-the-stack-be)
  *
  * <b>Possible values:</b> Any positive 32 bit integer. <br>
  * <b>Default value:</b> Varies by platform