ripgrep: use exit code 2 to indicate error

Exit code 1 was shared to indicate both "no results" and "error." Use
status code 2 to indicate errors, similar to grep's behavior.

Fixes #948 

PR #954

src/main.rs

@@ -60,7 +60,7 @@ fn main() {
         Ok(_) => process::exit(0),
         Err(err) => {
             eprintln!("{}", err);
-            process::exit(1);
+            process::exit(2);
         }
     }
 }