bug #11315 Linked the new Traverse article from an index (javiereguiluz)

This PR was submitted for the master branch but it was merged into the 3.4 branch instead (closes #11315).

Discussion
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Linked the new Traverse article from an index

Travis build is failing because of this.

Commits
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a59cad2 Linked the new Traverse article from an index

Author: wouterj

reference/constraints.rst

@@ -58,6 +58,7 @@ Validation Constraints Reference
    constraints/All
    constraints/UserPassword
    constraints/Valid
+   constraints/Traverse
 
 The Validator is designed to validate objects against *constraints*.
 In real life, a constraint could be: "The cake must not be burned". In

reference/constraints/map.rst.inc

@@ -78,3 +78,4 @@ Other Constraints
 * :doc:`Collection </reference/constraints/Collection>`
 * :doc:`Count </reference/constraints/Count>`
 * :doc:`UniqueEntity </reference/constraints/UniqueEntity>`
+* :doc:`Traverse </reference/constraints/Traverse>`