Ignore outer shadowing of throwaway variables

closes #67

spec/ameba/rule/lint/shadowing_local_outer_var_spec.cr

@@ -138,6 +138,19 @@ module Ameba::Rule::Lint
       subject.catch(source).should be_valid
     end
 
+    it "doesn't report if it shadows throwaway arguments" do
+      source = Source.new %(
+        data = [{1, "a"}, {2, "b"}, {3, "c"}]
+
+        data.each do |_, string|
+          data.each do |number, _|
+            puts string, number
+          end
+        end
+      )
+      subject.catch(source).should be_valid
+    end
+
     it "reports rule, location and message" do
       source = Source.new %(
         foo = 1

src/ameba/rule/lint/shadowing_local_outer_var.cr

@@ -53,6 +53,7 @@ module Ameba::Rule::Lint
 
     private def find_shadowing(source, scope)
       scope.arguments.each do |arg|
+        next if arg.ignored?
         if scope.outer_scope.try &.find_variable(arg.name)
           issue_for arg, MSG % arg.name
         end