Include stdbool.h for NRF52

Fixes https://github.com/cesanta/mjs/issues/82
Integrates https://github.com/cesanta/mjs/pull/85

PUBLISHED_FROM=2f5f50c25ec1c92fdfb783cd95cb57f0cb20642b

mongoose.h

@@ -1085,6 +1085,7 @@ int gettimeofday(struct timeval *tp, void *tzp);
 #include <ctype.h>
 #include <errno.h>
 #include <inttypes.h>
+#include <stdbool.h>
 #include <stdint.h>
 #include <string.h>
 #include <time.h>