Fix documentation referring to CertificateBuilder.set_version
diff --git a/docs/x509/reference.rst b/docs/x509/reference.rst
index b6c2f8a..e4ea252 100644
--- a/docs/x509/reference.rst
+++ b/docs/x509/reference.rst
@@ -393,7 +393,7 @@
 
 .. class:: CertificateBuilder
 
-    .. method:: set_version(version)
+    .. method:: version(version)
 
         Sets the X.509 version that will be used in the certificate.