build-unit-test-docker: Update valijson to v0.4

v0.4 contains 66262bafb82c ("Include nlohmann/json.hpp instead of
json.hpp") which resolves some subproject build issues with
entity-manager.

Change-Id: Ic1817abe0ac022b4cb1afed67aa6ac8a649519d0
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
1 file changed