Don't crash if modifying multiple profile files

src/rustup-cli/self_update.rs

@@ -86,9 +86,9 @@ macro_rules! pre_install_msg_unix {
     () => {
 pre_install_msg_template!(
 "This path will then be added to your `PATH` environment variable by
-modifying the profile file located at:
+modifying the profile file{plural} located at:
 
-    {rcfiles}"
+{rcfiles}"
     )};
 }
 
@@ -492,10 +492,13 @@ fn pre_install_msg(no_modify_path: bool) -> Result<String> {
                         None
                     }
                 }).collect::<Vec<_>>();
-            assert_eq!(rcfiles.len(), 1); // Only modifying .profile
+            let plural = if rcfiles.len() > 1 { "s" } else { "" };
+            let rcfiles = rcfiles.into_iter().map(|f| format!("    {}", f)).collect::<Vec<_>>();
+            let rcfiles = rcfiles.join("\n");
             Ok(format!(pre_install_msg_unix!(),
                        cargo_home_bin = cargo_home_bin.display(),
-                       rcfiles = rcfiles[0]))
+                       plural = plural,
+                       rcfiles = rcfiles))
         } else {
             Ok(format!(pre_install_msg_win!(),
                        cargo_home_bin = cargo_home_bin.display()))