src/meta-openembedded:cjson: upgrade 1.7.14 -> 1.7.15

Fixes:
Fix potential core dumped for strrchr, see DaveGamble/cJSON#546
Fix null pointer crash in cJSON_CreateXxArray, see DaveGamble/cJSON#538
Fix several null pointer problems on allocation failure, see DaveGamble/cJSON#526
Fix a possible dereference of null pointer, see DaveGamble/cJSON#519
Fix windows build failure about defining nan, see DaveGamble/cJSON#518

Signed-off-by: Wang Mingyu <[email protected]>
Signed-off-by: Khem Raj <[email protected]>