Fix malformed reST (#1802)
Commit 2b045757b560 ("Improve documentation related to inheritance. (#1676)") left off
a ':' from a hyperlink, which breaks the Travis CI build.
diff --git a/docs/advanced/classes.rst b/docs/advanced/classes.rst
index d1f8849..c9a0da5 100644
--- a/docs/advanced/classes.rst
+++ b/docs/advanced/classes.rst
@@ -325,7 +325,7 @@
Extended trampoline class functionality
=======================================
-.. _extended_class_functionality_forced_trampoline
+.. _extended_class_functionality_forced_trampoline:
Forced trampoline class initialisation
--------------------------------------