Fix link from CxxString::as_ptr to len method
diff --git a/src/cxx_string.rs b/src/cxx_string.rs
index baad468..54fad27 100644
--- a/src/cxx_string.rs
+++ b/src/cxx_string.rs
@@ -58,9 +58,10 @@
/// Note that the return type may look like `const char *` but is not a
/// `const char *` in the typical C sense, as C++ strings may contain
/// internal null bytes. As such, the returned pointer only makes sense as a
- /// string in combination with the length returned by [`len()`](#len).
+ /// string in combination with the length returned by [`len()`][len].
///
/// [data]: https://en.cppreference.com/w/cpp/string/basic_string/data
+ /// [len]: #method.len
pub fn as_ptr(&self) -> *const u8 {
unsafe { string_data(self) }
}