Fix DeclarationOrder false positives

As of Ruby 2.2.0 the sorting algorithm appears to have changed, which
results in an unstable sort of elements. These causes a false positive
since two nodes of the same type could have their order shuffled.

Fix this by including the index of the node in the sort so we preserve
order explicitly.

Author: sds

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## master (unreleased)
 
 * Fix `PropertyUnits` to not error on properties with function call values
+* Fix `DeclarationOrder` false positives on lines of the same type of node
 
 ## 0.36.0
 

lib/scss_lint/linter/declaration_order.rb

@@ -34,11 +34,12 @@ def important_node?(node)
     end
 
     def check_node(node)
-      children = node.children.select { |n| important_node?(n) }
-                              .map { |n| [n, node_declaration_type(n)] }
+      children = node.children.each_with_index
+                              .select { |n, _| important_node?(n) }
+                              .map { |n, i| [n, node_declaration_type(n), i] }
 
-      sorted_children = children.sort do |(_, a_type), (_, b_type)|
-        DECLARATION_ORDER.index(a_type) <=> DECLARATION_ORDER.index(b_type)
+      sorted_children = children.sort do |(_, a_type, i), (_, b_type, j)|
+        [DECLARATION_ORDER.index(a_type), i] <=> [DECLARATION_ORDER.index(b_type), j]
       end
 
       check_children_order(sorted_children, children)