fix typo

Author: lislis

locales/en-US/learn.ftl

@@ -74,7 +74,7 @@ learn-play-button = Try Rust without installing
 
 learn-install-rustup-header = Rustup: the Rust installer and version management tool
 learn-install-rustup = The primary way that folks install Rust is through a tool called Rustup, which is a Rust installer and version management tool.
-learn-install-rustup-update-header = Rustup do date?
+learn-install-rustup-update-header = Rustup to date?
 learn-install-rustup-update = Rust updates very frequently. If you have installed Rustup some time ago, chances are your Rust version is out of date. Get the latest version of Rust by running
 learn-install-rustup-button = Learn more about installation