Fix tfenv-min-required

[tskinn]

A recent PR seems to have broken min-required functionlaiy. #203 Attempting to fix here.

Example behavior seen currently (run from a terraform project directory):

$ grep -h required_version --include '*tf' "${PWD}"/* || grep -h -R required_version --include '*tf' "${PWD}"/* | grep  -o '\([0-9]\+\.\?\)\{2,3\}\(-[a-z]\+[0-9]\+\)\?'
  required_version = ">= 0.13.2"

Behavior after changes in this PR:

$ echo $(grep -h required_version --include '*tf' "${PWD}"/* || grep -h -R required_version --include '*tf' "${PWD}"/*) | grep  -o '\([0-9]\+\.\?\)\{2,3\}\(-[a-z]\+[0-9]\+\)\?'
0.13.2

[ndouglas]

I can confirm this fixed the issue for me locally.

[Zordrak]

Confirmed fixes #231