fix version redirects (#127)

Author: jordan-smith721

config/redirects

@@ -1,6 +1,6 @@
 define: prefix docs/drivers/csharp
 define: base https://www.mongodb.com/${prefix}
-define: versions 2.19 2.20 2.21 master
+define: versions v2.19 v2.20 v2.21 master
 
 raw: ${prefix}/ -> ${base}/current/
 raw: ${prefix}/stable -> ${base}/current/