Update README.markdown

Co-authored-by: Datong Sun <dndx@idndx.com>

Author: chronolaw

README.markdown

@@ -7760,7 +7760,7 @@ function provided by lua-resty-core.
 If both of `cert` and `pkey` are `nil`, this method will clear
 the client certificate and private key that were setted before.
 
-This method was first introduced in the `v0.10.21` release.
+This method was first introduced in the `v0.10.22` release.
 
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