Update TRPL/Installing Rust to avoid concrete version numbers

As discussed in PR rust-lang#28817

Author: dcarral

src/doc/trpl/installing-rust.md

@@ -84,16 +84,11 @@ If you've got Rust installed, you can open up a shell, and type this:
 $ rustc --version
 ```
 
-You should see the version number, commit hash, and commit date. If you just
-installed version 1.2.0, you should see:
+You should see the version number, commit hash, and commit date.
 
-```bash
-rustc 1.2.0 (082e47636 2015-08-03)
-```
-
-If you did, Rust has been installed successfully! Congrats!
+If you do, Rust has been installed successfully! Congrats!
 
-If you didn't and you're on Windows, check that Rust is in your %PATH% system
+If you don't and you're on Windows, check that Rust is in your %PATH% system
 variable. If it isn't, run the installer again, select "Change" on the "Change,
 repair, or remove installation" page and ensure "Add to PATH" is installed on
 the local hard drive.