json-glib: upgrade 1.6.6 -> 1.8.0

json-glib: upgrade 1.6.6 -> 1.8.0

Overview of changes for 1.8
==============================
* Build fixes
* Add current node accessor to JsonReader
* Make xgettext optional
* Avoid leaking memory in error paths
* Update test suite to conform with TAP
* Ensure valid output for exponential notation of numbers
* Translation updates

Signed-off-by: Yi Zhao <yi.zhao@windriver.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>