Texttable will try to detect the column type automatically, which
results in a low precision of the float that it is showing. We need to
disable that auto-formatting and just use `str(val)` instead.
Makes it easier to use in shell scripts. E.g. `-z $(dvc metrics diff)`, which
has the same semantics as `git diff`. Also syncs up with the behaviour
of `dvc diff`.
Fixes#3469
Ruslan Kuprieiev
Ruslan Kuprieiev