Merge branch 'josh/fix-small-bug-in-exit-code' into 'master'

Fixed a small issue with thread_exit_code()

See merge request !1

threads/thread.c

@@ -258,7 +258,7 @@ thread_name (void)
 }
 
 /* Returns the exit code of the running thread. */
-const int *
+int
 thread_exit_code (void)
 {
   return thread_current()->exit_code;

threads/thread.h

@@ -123,7 +123,7 @@ void thread_unblock (struct thread *);
 struct thread *thread_current (void);
 tid_t thread_tid (void);
 const char *thread_name (void);
-const int *thread_exit_code (void);
+int thread_exit_code (void);
 
 void thread_exit (void) NO_RETURN;
 void thread_yield (void);