Fix typo.

doc/ext_ffi_semantics.html

@@ -816,7 +816,7 @@ vararg functions</a>.
 <p>
 Memory areas returned by C functions (e.g. from <tt>malloc()</tt>)
 must be manually managed, of course (or use
-<a href="ext_ffi_api.html#ffi_gc"><tt>ffi.gc()</tt></a>)). Pointers to
+<a href="ext_ffi_api.html#ffi_gc"><tt>ffi.gc()</tt></a>). Pointers to
 cdata objects are indistinguishable from pointers returned by C
 functions (which is one of the reasons why the GC cannot follow them).
 </p>