Missing parens in pretty printer for types

Apparently we got the precedences wrong in the pretty printer for Cryptol types:
```
Cryptol> :t [zero : Z 5]
[zero : Z 5] : [1]Z 5
```
This should be `[1](Z 5)` instead of `[1]Z 5`, because `[1]Z 5` doesn't parse:
```
Cryptol> [zero] : [1]Z 5

Parse error at <interactive>:1:15,
  unexpected: 5
```