Update Serialization Library submodule

To include:
* Allow adding placeholders without data
* Set warnings as errors
* Generate strict json by default when serializing
* Avoid supplying unsupported linker flags
* Use portable type with random engine

Change-Id: I5c04f85dc6608fb955bd84f5f7c5a1a3a7ef57b6
Signed-off-by: Jeremy Johnson <jeremy.johnson@arm.com>