server_version(); is unsupported in redshift

## redshift migration is not working because of unsupported function `server_version()`.
- [ ] Bug report

## Current behavior
Since redshift is postgres compliance, i'm using `db-migrate-pg` in my node.js application for `redshift`.

When i ran `migrate` script, i'm getting below error from redshift db.
Here is my verbose looks like:
```
sangeeth@sangeeth-kumar ~/Desktop/analytics-api $ ./node_modules/.bin/db-migrate up --config cfg/database.json --verbose
[INFO] Detected and using the projects local version of db-migrate. '/home/sangeeth/Desktop/analytics-api/node_modules/db-migrate/index.js'
[INFO] Using dev settings: { driver: 'pg',
database: 'analytics',
user: 'master',
password: '******',
host: '*****',
port: '****' }
[INFO] require: db-migrate-pg
[INFO] connecting
[INFO] connected
[SQL] show server_version_num
[SQL] show server_version
[ERROR] error: must be superuser to examine "server_version"
at Connection.parseE (/home/sangeeth/Desktop/analytics-api/node_modules/pg/lib/connection.js:553:11)
at Connection.parseMessage (/home/sangeeth/Desktop/analytics-api/node_modules/pg/lib/connection.js:378:19)
at Socket. (/home/sangeeth/Desktop/analytics-api/node_modules/pg/lib/connection.js:119:22)
at emitOne (events.js:116:13)
at Socket.emit (events.js:211:7)
at addChunk (_stream_readable.js:263:12)
at readableAddChunk (_stream_readable.js:250:11)
at Socket.Readable.push (_stream_readable.js:208:10)
at TCP.onread (net.js:607:20)
```
So we can see the error is thrown from `redshift`.

I had asked this in SO.
[Link to stackoverflow question](https://stackoverflow.com/questions/51422236/what-role-permission-needed-for-the-user-to-get-the-server-version-in-amazon-red)

Got to know that `show server_version();` is unsupported postgres function in redshift and they suggested to patch the library to work with `select version();` instead.
```
analytics=# select version();
version
--------------------------------------------------------------------------------------------------------------------------
PostgreSQL 8.0.2 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 3.4.2 20041017 (Red Hat 3.4.2-6.fc3), Redshift 1.0.2915
(1 row)

```
## Expected behavior
Can you help me out, how to migrate my sql scripts in redshift?
Or
How to patch `server_version` to use `select version`?

## Environment

db-migrate version: 0.11.1

db-migrate-pg: 0.4.0

redshift: 1.0.2915

PostgreSQL 8.0.2


Additional information:

- Node version: 8.11.1

- Platform:  Linux

---

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