change 'visibility' class to 'item-kind' in docs template

(cherry picked from commit 13b85c68484c709b5a81d7afe0db60aacf9f0bbb)

docs/contract.hbs

@@ -66,7 +66,7 @@
 {{#each modifiers}}
 [.contract-item]
 [[{{anchor}}]]
-==== `pass:normal[{{name}}({{> typed-variable-array args}})]` [.visibility]#modifier#
+==== `pass:normal[{{name}}({{> typed-variable-array args}})]` [.item-kind]#modifier#
 
 {{natspec.devdoc}}
 
@@ -75,7 +75,7 @@
 {{#each functions}}
 [.contract-item]
 [[{{anchor}}]]
-==== `pass:normal[{{name}}({{> typed-variable-array args}}){{#if outputs}} → {{> typed-variable-array outputs}}{{/if}}]` [.visibility]#{{visibility}}#
+==== `pass:normal[{{name}}({{> typed-variable-array args}}){{#if outputs}} → {{> typed-variable-array outputs}}{{/if}}]` [.item-kind]#{{visibility}}#
 
 {{natspec.devdoc}}
 
@@ -84,7 +84,7 @@
 {{#each events}}
 [.contract-item]
 [[{{anchor}}]]
-==== `pass:normal[{{name}}({{> typed-variable-array args}})]` [.visibility]#event#
+==== `pass:normal[{{name}}({{> typed-variable-array args}})]` [.item-kind]#event#
 
 {{natspec.devdoc}}