IWYU: Add mapping for jsoncpp version.h

Add an IWYU rule for `version.h` from `jsoncpp`. This mirrors the
existing rules that recommend `value.h` for things from `forwards.h` and
`config.h`, and is needed for IWYU to not complain about use of things
from `version.h`. (This is especially important as we do not directly
wrap `version.h`.)

Utilities/IWYU/mapping.imp

@@ -59,6 +59,7 @@
   { include: [ "@<.*curl/system.h>", private, "<cm3p/curl/curl.h>", public ] },
   { include: [ "@<.*json/config.h>", private, "<cm3p/json/value.h>", public ] },
   { include: [ "@<.*json/forwards.h>", private, "<cm3p/json/value.h>", public ] },
+  { include: [ "@<.*json/version.h>", private, "<cm3p/json/value.h>", public ] },
   { include: [ "@<.*uv/.+\\.h>", private, "<cm3p/uv.h>", public ] },
   { include: [ "@<.*expat_external.h>", private, "<cm3p/expat.h>", public ] },
   { include: [ "@<.*zconf.h>", private, "<cm3p/zlib.h>", public ] },