Enforce strict mode of jsmn.

Enforce strict mode of jsmn.

If no strict mode of jsmn is enforced, then the correct amount of
json elements would have to be checked to avoid segmentation faults
on malformed state files:

$ echo '{ "focusedMonitorId" }' > malformed-state
$ bspwm -s malformed-state
Segmentation fault
$ _

Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>