Handle relative source path in create_link #identical?

When creating a symlink, the source path may be relative to the destination. If
this is the case, #identical? fails becase it interprets it as an absolute path.
Update #identical to resolve the source path before comparing.

lib/thor/actions/create_link.rb

@@ -33,7 +33,8 @@ class CreateLink < CreateFile #:nodoc:
       # Boolean:: true if it is identical, false otherwise.
       #
       def identical?
-        exists? && File.identical?(render, destination)
+        source = File.expand_path(render, File.dirname(destination))
+        exists? && File.identical?(source, destination)
       end
 
       def invoke!

spec/actions/create_link_spec.rb

@@ -93,6 +93,18 @@ def revoke!
       invoke!
       expect(action.identical?).to be true
     end
+
+    context "with source path relative to destination" do
+      let(:source) do
+        destination_path = File.dirname(File.join(destination_root, destination))
+        Pathname.new(super()).relative_path_from(destination_path).to_s
+      end
+
+      it "returns true if the destination link exists and is identical" do
+        expect(action.identical?).to be false
+        invoke!
+        expect(action.identical?).to be true
+      end
     end
   end