missing error for **

```
julia> 2**3
ERROR: ParseError:
Error: invalid syntax atom
@ REPL[3]:1:2
2**3
Error: extra tokens after end of expression
@ REPL[3]:1:4
2**3
```
instead of
```
julia> 2**3
ERROR: syntax: use "x^y" instead of "x**y" for exponentiation, and "x..." instead of "**x" for splatting.
```
