Replace -- with —

Author: kini

src/doc/trpl/installing-rust.md

@@ -53,7 +53,7 @@ us an uninstall option.
 Some people, and somewhat rightfully so, get very upset when we tell them to
 `curl | sh`. Their concern is that `curl | sh` implicitly requires you to trust
 that the good people who maintain Rust aren't going to hack your computer and
-do bad things -- and even having accepted that, there is still the possibility
+do bad things — and even having accepted that, there is still the possibility
 that the Rust website has been hacked and the `rustup` script compromised.
 
 Being wary of such possibilities is a good instinct! If you're uncomfortable