build specifically with FreeRTOS 10.6.2
Before this small change, the PicoHTTPServer project would try to build against the development version of FreeRTOS (the tip of the master branch). At the current time this branch is in flux and PicoHTTPServer does not build.
This commit specifies the exact version of FreeRTOS to build against as 10.6.2 (the most recent stable version), which I've verified works.
A better solution might be to use FreeRTOS as a submodule, so that the PicoHTTPServer repo can explicitly control the FreeRTOS version, instead of relying on the build script to select one.
Let me know if you'd prefer a PR that makes FreeRTOS a submodule of PicoHTTPServer. I think that would be a better long term solution.
For the record, this PR was prompted by the same error that @paulmreese fixed in #1, but this solution picks a specific release to build against and doesn't try to adapt PicoHTTPServer to the changing main development branch of FreeRTOS.