build: ignore googleapis.com in doc link check (#368)

Author: jkwlui

.kokoro/docs.sh

@@ -30,4 +30,4 @@ BIN=./node_modules/.bin
 npm install broken-link-checker
 npm install http-server
 $BIN/http-server -p 8080 docs/ &
-$BIN/blc -r http://localhost:8080
+$BIN/blc http://localhost:8080 -r --exclude www.googleapis.com