Add newline for stderr messages

[apoorvdeshmukh]

This commit addresses issue #102.
stderr messages when redirected to stdout would not contain the EOL, causing the prompt to appear on the line as the stderr message.

With existing go-sqlcmd

$ sqlcmd -r0
1> select @@version1
2> go
Must declare the scalar variable "@@version1".1>

After the changes in PR

git\go-sqlcmd>sqlcmd -r0
1> select @@version1
2> go
Must declare the scalar variable "@@version1".
1>