Update index.bs

Co-authored-by: Jan-Ivar Bruaroey <jan-ivar@users.noreply.github.com>

Author: youennf

index.bs

@@ -368,7 +368,7 @@ The <dfn method for="SFrameEncrypterKeyManager">setEncryptionKey(|key|, |keyID|)
     1. [=Queue a task=] to [=resolve=] |promise| with undefined.
 1. Return |promise|.
 
-The <dfn method for="SFrameDecrypterKeyManager">addEncryptionKey(|key|, |keyID|)</dfn> method steps are:
+The <dfn method for="SFrameDecrypterKeyManager">addDecryptionKey(|key|, |keyID|)</dfn> method steps are:
 1. Let |promise| be [=a new promise=].
 1. If |keyID| is a {{bigint}} which cannot be represented as a integer between 0 and 2<sup>64</sup>-1 inclusive, [=reject=] |promise| with a {{RangeError}} exception, and abort these steps..
 1. [=In parallel=], run the following steps: