threaded-shared-conn.c: fixed typo in commenta

 * This example fires up NUM_THREADS threads and in each single thread, it

 * downloads the same fixed URL a URL_ITERATIONS number of times. The received

 * data is just thrown away. It sets up a single shared object that holds the

 * connection cache and all easy threads in all threads share that same cache.

 * connection cache and all easy handles in all threads share that same cache.

 *

 * This example uses pthreads for threads and mutexes, but should be easy to

 * modify to use different thread/mutex system should you want to.