Update index.bs (test) (#653)

privacy-preserving (purely editorial, to test whether PR-preview is generating)

Author: wseltzer

Diff for: spec/index.bs

@@ -19,7 +19,7 @@ Text Macro: TRUE <code>true</code>
 Text Macro: RP Relying Party
 Text Macro: IDP Identity Provider
 
-Abstract: A Web Platform API that allows users to login to websites with their federated accounts in a privacy preserving manner.
+Abstract: A Web Platform API that allows users to login to websites with their federated accounts in a privacy-preserving manner.
 
 Test Suite: https://github.com/web-platform-tests/wpt/tree/master/fedcm
 </pre>