Fixed typo

It seems the word "checks" was misspelled as "checkes".

test/unit/support.js

@@ -30,7 +30,7 @@ if ( jQuery.css ) {
 	});
 }
 
-// This test checkes CSP only for browsers with "Content-Security-Policy" header support
+// This test checks CSP only for browsers with "Content-Security-Policy" header support
 // i.e. no old WebKit or old Firefox
 testIframeWithCallback( "Check CSP (https://developer.mozilla.org/en-US/docs/Security/CSP) restrictions",
 	"support/csp.php",