fix a typo.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@18988 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

thread.c

@@ -932,7 +932,7 @@ rb_thread_blocking_region(
     rb_thread_t *th = GET_THREAD();
 
     if (ubf == RUBY_UBF_IO || ubf == RUBY_UBF_PROCESS) {
-	ubf = ubf_select;n
+	ubf = ubf_select;
 	data2 = th;
     }