Add suggestion to use "no-cors" with Fetch fails CORS check.

LayoutTests/http/tests/htmlimports/import-script-block-crossorigin-dynamic-expected.txt

-CONSOLE ERROR: Script from origin 'http://127.0.0.1:8000' has been blocked from loading by Cross-Origin Resource Sharing policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8000' is therefore not allowed access.
-CONSOLE ERROR: Script from origin 'http://127.0.0.1:8000' has been blocked from loading by Cross-Origin Resource Sharing policy: The 'Access-Control-Allow-Origin' header has a value 'http://127.0.0.1:8000' that is not equal to the supplied origin. Origin 'http://localhost:8000' is therefore not allowed access.
+CONSOLE ERROR: Script from origin 'http://127.0.0.1:8000' has been blocked from loading by Cross-Origin Resource Sharing policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8000' is therefore not allowed access. Alternatively, if you want an opaque response, switch to The Fetch API in 'no-cors' mode.
+CONSOLE ERROR: Script from origin 'http://127.0.0.1:8000' has been blocked from loading by Cross-Origin Resource Sharing policy: The 'Access-Control-Allow-Origin' header has a value 'http://127.0.0.1:8000' that is not equal to the supplied origin. Origin 'http://localhost:8000' is therefore not allowed access. Either change the header, or, if you want an opaque response, use the Fetch API in 'no-cors' mode.
 This test ensures that crossorigin-marked script elements are blocked properly
 
 On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
 
 
 PASS document.externalScriptHasRun is undefined
 PASS document.corsExternalScriptHasRun is undefined
 PASS document.corsExternalScriptForLocalhostHasRun is true
 PASS successfullyParsed is true
 
 TEST COMPLETE