upgrade dependencies.

This is what it did (and didn't) do.  I don't see a need to upgrade syn
and pretttyplease to a possibly breaking version right now.  Can do that
post-1.0.0:

```
name         old req compatible latest  new req note
====         ======= ========== ======  ======= ====
serde        1.0.156 1.0.159    1.0.159 1.0.159
serde_json   1.0.94  1.0.95     1.0.95  1.0.95
tempfile     3.4.0   3.5.0      3.5.0   3.5.0
prettyplease 0.1     0.1.25     0.2.4   0.1     incompatible
syn          1       1.0.109    2.0.13  1       incompatible
omnipath     0.1.1   0.1.5      0.1.5   0.1.5
memfd        0.6.2   0.6.3      0.6.3   0.6.3
```