Update Cargo.toml

Author: mailboxvalidator-com

Cargo.toml

@@ -9,9 +9,9 @@ readme = "readme.md"
 homepage = "https://github.com/MailboxValidator/mailboxvalidator-rust"
 repository = "https://github.com/MailboxValidator/mailboxvalidator-rust/"
 license = "MIT"
+license-file = "LICENSE.txt"
 keywords = ["email", "validation", "validator", "free", "disposable"]
 categories = ["email", "accessibility"]
-readme = "readme.md"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html