Add support for pg 7.x

[matt-oakes]

No description provided.

[kjin]

@matt-oakes Thanks for the PR! Mind if I rebase + commit to your pg-version branch?

[matt-oakes]

@kjin No problem at all!

[codecov]

Codecov Report

Merging #701 into master will decrease coverage by 0.15%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #701      +/-   ##
==========================================
- Coverage   91.02%   90.87%   -0.16%     
==========================================
  Files          29       29              
  Lines        1437     1435       -2     
  Branches      280      280              
==========================================
- Hits         1308     1304       -4     
  Misses         52       52              
- Partials       77       79       +2

Impacted Files	Coverage Δ
src/plugins/plugin-pg.ts	76.66% <100%> (ø)	⬆️
src/index.ts	90.14% <0%> (-1.64%)	⬇️
src/trace-writer.ts	89.83% <0%> (-0.85%)	⬇️
src/trace-api.ts	94.25% <0%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4d3d54e...ae3abfa. Read the comment docs.

[kjin]

@matt-oakes The upgrade guide for PG 7 suggests that there are some API changes that aren't covered in the current plugin implementation. Would you be interested in amending your PR to support these API changes? If not -- that's totally fine, I'll merge this PR and open a new one imminently to support those changes. (I've gone through the upgrade guide just now so I think I have a pretty good idea of what needs to be changed.)

[matt-oakes]

@kjin Would it be possible for you to do it. I haven't got too much experience with either this module or the pg module itself (I use it through a wrapper) so I don't trust myself not to mess it up.

Thanks!

[kjin]

Sure thing. I'll go ahead an merge this PR then!