build: update default FREETDS_VERSION to track the latest release of tiny_tds

[bf4]

Right now we default FREETDS_VERSION to 1.00.109
but the latest tiny_tds release, v3.2.0 uses 1.4.26

We should track the FREETDS_VERSION in this repo against the latest build used by tiny_tds
At a minimum, it removes a possible source of segmentation faults

[andyundso]

likely this buildpack is not even needed anymore, since there is a precompiled version of the gem on Linux with the FreeTDS dependency built-in.

[bf4]

Agreed, though when I removed it, some connections began failing, and I ended up restoring it.
Ref rails-sqlserver/tiny_tds#588