Use snprintf instead of sprintf (#2111)

src/catch2/reporters/catch_reporter_combined_tu.cpp

@@ -44,7 +44,7 @@ namespace Catch {
 #ifdef _MSC_VER
         sprintf_s( buffer, "%.3f", duration );
 #else
-        std::sprintf( buffer, "%.3f", duration );
+        std::snprintf( buffer, maxDoubleSize, "%.3f", duration );
 #endif
         return std::string( buffer );
     }