Setting PostgreSQL 9.5 as the main version to test against.

NOTE: The following settings are required for 9.5 to work:
```
sudo: required
dist: trusty
```

* Use container-based CI

* Remove unnecessary CI configuration

* Use Node 6/PostgreSQL 9.6 as default test

… rather than testing 0.10 twice with unspecified PostgreSQL.

* Use `precise` for PostgreSQL 9.1

According to https://docs.travis-ci.com/user/database-setup/, 9.1 isn’t supported on trusty.

* Fix Node 0.10 and 0.12 CI builds

These binaries appear to have been built using g++ with flags that clang doesn’t support. Or something.

It’s not JSON.

This functionality is already tested in the node-pg-types repo.