update release notes for next release (change missed from 0.9.20)

kares · kares · commit 2e70c2b0a1c1 · 2017-03-03T09:43:54.000+01:00
diff --git a/History.md b/History.md
@@ -1,3 +1,7 @@
+## 0.9.21.dev
+
+* add support for renegotiation_cb on SSLContext (#121)
+
 ## 0.9.20
 
 * upgrade Bouncy-Castle to 1.56 http://bouncycastle.org/releasenotes.html
