Marking plugins_publish with PY2+3

Bug:1256595
Change-Id: I28e461741461f549c31f2da0bf3c2f2f3e2057af
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/18827
Reviewed-by: Godofredo Contreras <godofredoc@google.com>
Commit-Queue: Yusuf Mohsinally <mohsinally@google.com>
diff --git a/recipes/plugins/plugins_publish.py b/recipes/plugins/plugins_publish.py
index 51acf51..6fad25b 100644
--- a/recipes/plugins/plugins_publish.py
+++ b/recipes/plugins/plugins_publish.py
@@ -2,6 +2,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+PYTHON_VERSION_COMPATIBILITY = 'PY2+3'
+
 DEPS = [
     'recipe_engine/step',
 ]
@@ -12,4 +14,4 @@
     api.step('report', ['echo', 'Complete publishing plugins (tests)]'])
 
 def GenTests(api):
-  yield api.test('basic')
\ No newline at end of file
+  yield api.test('basic')