Increment floats

[thecodeboss]

Fixes #868 and #1990.

For a query such as:

knex('accounts').where('id', 1).increment('balance', 0.1);

the expected sql is

update "accounts" set "balance" = "balance" + 0.1 where "id" = 1

however, the actual sql is

update "accounts" set "balance" = "balance" + 0 where "id" = 1

The problem is that parseInt is being used instead of parseFloat in the builder code.

I tried my best to write lots of tests, and I had to add a float column to the existing integration test account schema to properly test this. This is my first time contributing to this repo, so apologies if I missed anything in the process.

[elhigu]

Looks good 👍

[elhigu]

thanks a lot!