Fix semantic urls for function and modifier overriding in documentation

docs/contracts/inheritance.rst

@@ -194,10 +194,10 @@ not known in the context of the class where it is used,
 although its type is known. This is similar for ordinary
 virtual method lookup.
 
-.. _function-overriding:
-
 .. index:: ! overriding;function
 
+.. _function-overriding:
+
 Function Overriding
 ===================
 
@@ -317,10 +317,10 @@ of the variable:
   While public state variables can override external functions, they themselves cannot
   be overridden.
 
-.. _modifier-overriding:
-
 .. index:: ! overriding;modifier
 
+.. _modifier-overriding:
+
 Modifier Overriding
 ===================