feat: changed username generator fix

tmpmail

@@ -81,7 +81,7 @@ generate_email_address() {
     # So charcters such as dashes, periods, underscore, and numbers are all deleted,
     # giving us a text which only contains lower case letters form A to Z. We then take
     # the first 10 characters, which will be the username of the email address
-    USERNAME=$(date +%s | base64 | tr -dc '[[:alnum:]]' | tr '[:upper:]' '[:lower:]')
+    USERNAME=$(date +%s | base64 | tr -dc "[:alnum:]" | tr "[:upper:]" "[:lower:]")
 
     # Valid TLDS which 1secmail provides.
     TLDS="com net org"