fix leak

```
840 (360 direct, 480 indirect) bytes in 15 blocks are definitely lost in loss record 55 of 55
  /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so   calloc
                                   ht.c:22   w_ht_new
                                root.c:325   root_resolve
                               root.c:2801   w_root_resolve
                            listener.c:410   resolve_root_or_err
                                watch.c:86   cmd_watch
                            listener.c:509   dispatch_command
                            listener.c:566   client_thread
                      pthread_create.c:308   start_thread
```
Fixed typos

Resolves https://github.com/facebook/watchman/pull/18

applied using `hub am https://github.com/facebook/watchman/pull/18`