use "std" namespace for "sprintf"

[girtsf]

Some compilers don't export C compatibility functions in ::. Using
std::sprintf should work for those (and all other compilers).

Reference: https://en.cppreference.com/w/cpp/header#C_compatibility_headers

[codecov]

Codecov Report

Merging #1541 into master will not change coverage.
The diff coverage is 0%.

@@          Coverage Diff           @@
##           master   #1541   +/-   ##
======================================
  Coverage    80.6%   80.6%           
======================================
  Files         121     121           
  Lines        3386    3386           
======================================
  Hits         2729    2729           
  Misses        657     657

[codecov]

Codecov Report

Merging #1541 into master will not change coverage.
The diff coverage is 0%.

@@          Coverage Diff           @@
##           master   #1541   +/-   ##
======================================
  Coverage    80.6%   80.6%           
======================================
  Files         121     121           
  Lines        3386    3386           
======================================
  Hits         2729    2729           
  Misses        657     657

[horenmar]

Thanks. We generally make an attempt at consistently using the std:: prefix (and the <cfoo> form of C headers), but it sometimes creeps in. The only platform I know of that actually cares about the difference is QNX and it is kinda hard to get a CI using it.

[girtsf]

Thanks, @horenmar!

What we are using isn't QNX, but isn't too far off. It's something that starts with "vx" and ends with "works". :)

Catch2 works on it with two minor fixes:

1. this pull request
2. use ::std for tolower Clara#86 (just fixed it so that it now passes the appveyor windows builds too)

Thanks for the project!