pre-upload/pylint: drop support for Python 3.5

We've been emitting warnings about this for almost a year.

Bug: None
Test: `repo upload` still works w/Python 3.6
Change-Id: Iaead2a48ac125749176925302bf32e655384c965
diff --git a/pre-upload.py b/pre-upload.py
index 0e032f4..7eb11b8 100755
--- a/pre-upload.py
+++ b/pre-upload.py
@@ -26,8 +26,8 @@
 
 
 # Assert some minimum Python versions as we don't test or support any others.
-if sys.version_info < (3, 5):
-    print('repohooks: error: Python-3.5+ is required', file=sys.stderr)
+if sys.version_info < (3, 6):
+    print('repohooks: error: Python-3.6+ is required', file=sys.stderr)
     sys.exit(1)