Improve documentation changes of a recent commit

* doc/lispref/text.texi (Parsing JSON): Improve wording of the
documentation of 'json-parse-string' and 'json-parse-buffer'.
* src/json.c (Fjson_parse_string, Fjson_parse_buffer): Doc fix.
1 job for master in 51 minutes and 38 seconds (queued for 1 second)
Status Job ID Name Coverage
failed #1328


Name Stage Failure
test-all Test
make[2]: *** [check-doit] Error 1
make[1]: *** [check-expensive] Error 2
Makefile:313: recipe for target 'check-doit' failed
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:288: recipe for target 'check-expensive' failed
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:962: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1