Update solutions/ownership/borrowing.md

Author: sunface

solutions/ownership/borrowing.md

@@ -147,7 +147,7 @@ fn main() {
     let r1 = &mut s;
     let r2 = &mut s;
 
-    // add one line below to make a compiler error: cannot borrow `s` as mutable more than once at a time
+    // Add one line below to make a compiler error: cannot borrow `s` as mutable more than once at a time
     // you can't use r1 and r2 at the same time
     println!("{}", r1);
 }