made changes according to shellcheck errors

tmpmail

@@ -87,6 +87,8 @@ 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
+    #
+    # shellcheck disable=SC2018
     USERNAME=$(head /dev/urandom | tr -dc a-z | cut -c1-11)
 
     # This is an array of the valid TLDS which 1secmail provides.
@@ -116,7 +118,7 @@ generate_email_address() {
 
     # Save the generated email address to the $TMPMAIL_EMAIL_ADDRESS file
     # so that it can be whenever 'tmpmail' is run
-    echo $EMAIL_ADDRESS >"$TMPMAIL_EMAIL_ADDRESS"
+    echo "$EMAIL_ADDRESS" >"$TMPMAIL_EMAIL_ADDRESS"
 
     # If this function was called because the user wanted to generate a new
     # email address, show them the email address