Fix wrong fwrite arguments order in example

Closes #132

Author: alexeyvo

examples/example-gridfs.c

@@ -61,7 +61,7 @@ int main (int argc, char *argv[])
             break;
          }
 
-         if (fwrite (iov.iov_base, r, 1, stdout) != r) {
+         if (fwrite (iov.iov_base, 1, r, stdout) != r) {
             MONGOC_ERROR ("Failed to write to stdout. Exiting.\n");
             exit (1);
          }