[API] Generator: Fix regexp for docs url

Author: picandocodigo

elasticsearch-api/utils/thor/templates/_documentation_top.erb

@@ -24,5 +24,5 @@
 <% end -%>
 <%= '  '*(@namespace_depth+3) -%>#
 <%# Documentation link -%>
-<%=  '  '*(@namespace_depth+3) %># @see <%= @spec['documentation']['url'] ? @spec['documentation']['url'].gsub(/\/current|master\//, "#{Elasticsearch::API::FilesHelper.gem_version}/") : "[TODO]" %>
+<%=  '  '*(@namespace_depth+3) %># @see <%= @spec['documentation']['url'] ? @spec['documentation']['url'].gsub(/\/(current|master)\//, "/#{Elasticsearch::API::FilesHelper.gem_version}/") : "[TODO]" %>
 <%= '  '*(@namespace_depth+3) %>#