[thread.sema.cnt] "Class" -> "Class template" in description of a class

template.

Author: zygoloid

source/threads.tex

@@ -4745,7 +4745,7 @@
 \end{codeblock}
 
 \pnum
-Class \tcode{counting_semaphore} maintains an internal counter
+Class template \tcode{counting_semaphore} maintains an internal counter
 that is initialized when the semaphore is created.
 The counter is decremented when a thread acquires the semaphore, and
 is incremented when a thread releases the semaphore.