Remove bad assert. (#11)

We reserve bufmaxlen bytes in the string, but then proceed to push
up to bufmaxlen chars. Therefore it is possible that the string will
need to reallocate. A different solution would be to reserve
4*bufmaxlen bytes. Removing the assert is probably ok, because the
attempt to pre-allocate is just a performance optimization.

parser/src/scanner.rs

@@ -2230,7 +2230,6 @@ impl<T: Input> Scanner<T> {
                             end = true;
                             break;
                         }
-                        assert!(string.len() < string.capacity());
                         string.push(self.input.peek());
                         self.skip_non_blank();
                     }