README: Remove note about not supporting EAB. (#328)

Since #288 Pebble **does**
support external account binding (EAB). This commit updates the
"Limitations" section of the README accordingly.

Author: cpu

README.md

@@ -53,9 +53,9 @@ clients are not hardcoding URLs.)
 ## Limitations
 
 Pebble is missing some ACME features (PRs are welcome!). It does not presently
-support subproblems, pre-authorization or external account binding. Pebble does
-not support revoking a certificate issued by a different ACME account by proving
-authorization of all of the certificate's domains.
+support subproblems, or pre-authorization. Pebble does not support revoking a 
+certificate issued by a different ACME account by proving authorization of all
+of the certificate's domains.
 
 Pebble does not perform all of the same input validation as Boulder. Some domain
 names that would be rejected by Boulder/Let's Encrypt may work with Pebble.