Upgrade python/google-api-python-client to v1.8.1

Exempt-From-Owner-Approval: upgrade
Change-Id: Ie770a5d7d89d86764cbd530c46f809805c62e9ea
diff --git a/METADATA b/METADATA
index 440c5d9..cd76b0c 100644
--- a/METADATA
+++ b/METADATA
@@ -9,10 +9,10 @@
     type: GIT
     value: "https://github.com/google/google-api-python-client"
   }
-  version: "v1.7.12"
+  version: "v1.8.1"
   last_upgrade_date {
     year: 2020
-    month: 3
-    day: 11
+    month: 4
+    day: 20
   }
 }