fix(encode64): use proper encode file flags

Fixes #12509

plugins/encode64/encode64.plugin.zsh

@@ -10,7 +10,7 @@ encodefile64() {
     if [[ $# -eq 0 ]]; then
         echo "You must provide a filename"
     else
-        base64 -i $1 -o $1.txt
+        base64 $1 > $1.txt
         echo "${1}'s content encoded in base64 and saved as ${1}.txt"
     fi
 }