Small improvement as proposed by Vanand Gasparyan

Author: josuttis

source/jthread.hpp

@@ -76,7 +76,7 @@ class jthread
   private:
     //*** API for the starting thread:
     stop_source _stopSource;                   // stop_source for started thread
-    ::std::thread _thread{::std::thread{}};    // started thread (if any)
+    ::std::thread _thread{};                   // started thread (if any)
 };