Fix line endings

Before this change, samples in the Rust book looked like this:

fn main() {

    println!("hello world!");

}

Afterward, it looks like this, which is correct,

fn main() {
    println!("hello world");
}

Basically, when you use parse_line, syntect implicitly inserts the line breaks.

Author: notriddle

src/utils/highlight.rs

@@ -125,7 +125,6 @@ fn boringify(line: &str) -> (String, bool) {
         }
     }
     result += line;
-    result += "\n";
 
     (result, false)
 }