Remove information in README about issues with TDS version at login

[andyundso]

Closes #447

I quickly tested setting the TDS version manually on client initialization and it seems to work as expected. tds_version is implemented in C and asks the dbproc struct about the used version, so this information should be reliable.

irb(main):001> require "tiny_tds"
=> true
irb(main):002* client = TinyTds::Client.new({
irb(main):003*     username: "tinytds",
irb(main):004*     password: "",
irb(main):005*     host: "127.0.0.1",
irb(main):006*     tds_version: "7.3"
irb(main):007> })
=> 
#<TinyTds::Client:0x0000767d1cb58f00
...
irb(main):008> client.tds_version
=> 11
irb(main):009* client = TinyTds::Client.new({
irb(main):010*     username: "tinytds",
irb(main):011*     password: "",
irb(main):012*     host: "127.0.0.1",
irb(main):013*     tds_version: "7.4"
irb(main):014> })
=> 
#<TinyTds::Client:0x0000767d1cb50670
...
irb(main):015> client.tds_version
=> 12