Fix typo in how_nushell_code_gets_run.md (#1916)

Author: gigi4000august

book/how_nushell_code_gets_run.md

@@ -52,7 +52,7 @@ fn main() {
 To "run" this code, it must be:
 
 1. Compiled into [machine code instructions](https://en.wikipedia.org/wiki/Machine_code)
-2. The compilation results stored as a binary file one the disk
+2. The compilation results stored as a binary file on the disk
 
 The first two steps are handled with `rustc main.rs`.