[config.c] use intmax_t to fix warning across platforms

fixes:
  config.c:186:56: warning: format specifies type 'long' but the argument
    has type 'uint64_t' (aka 'unsigned long long') [-Wformat]
    err("error parsing %s at %ld near:", filename, whence);
Merge pull request #132 from ChrisLundquist/fix-printf-warning

[config.c] fix printf format string warning