Add credit to bug2752; correct the issue number in the changes file

changes/bug2752

-  o Minor bugfixes
+  o Minor features:
     - Tor used to limit HttpProxyAuthenticator values to 48 characters.
     Changed the limit to 512 characters by removing base64 newlines.
-    Fixes bug 2917.
+    Fixes bug 2752.  Fix by Michael Yakubovich.