fixes guard macro for use of std::put_time

std::put_time is in the c++11 iomanip header not chrono

changelog.md

@@ -28,6 +28,10 @@ HEAD
 - Improvement: Core library no longer has std::iostream as a dependency.
   std::iostream is still required for the optional iostream logging policy and
   iostream transport.
+- Bug: C++11 Chrono support was being incorrectly detected by the `boost_config`
+  header. Thank you Max Dmitrichenko for reporting and a patch.
+- Bug: use of `std::put_time` is now guarded by a general 11 flag rather than
+  a chrono flag. Thank you Max Dmitrichenko for reporting.
 - Compatibility: Adjust usage of std::min to be more compatible with systems
   that define a min(...) macro.
 - Compatibility: Removes unused parameters from all library, test, and example

websocketpp/logger/basic.hpp

@@ -133,7 +133,7 @@ private:
     static std::ostream & timestamp(std::ostream & os) {
         std::time_t t = std::time(NULL);
         std::tm* lt = std::localtime(&t);
-        #ifdef _WEBSOCKETPP_CPP11_CHRONO_
+        #ifdef _WEBSOCKETPP_CPP11_STL_
             return os << std::put_time(lt,"%Y-%m-%d %H:%M:%S");
         #else // Falls back to strftime, which requires a temporary copy of the string.
             char buffer[20];