Fix tfutils#301: find min-required version through -chdir

This commit makes it possible to use `min-required` with the terraform
configuration (including the `required_version` spec) in a subdirectory
as `terraform -chdir=subdir`.

Prior to this commit, this behaviour does not work (`-chdir` cannot be
used with `tfenv`'s `terraform` wrapper & `min-required` version)
because `tfenv` expects to find the configuration in `$PWD`.

bin/tfenv

@@ -60,8 +60,15 @@ done;
 
 declare arg="${1:-""}";
 
-log 'debug' "Setting TFENV_DIR to ${PWD}";
-export TFENV_DIR="${PWD}"
+for _arg in ${@:1}; do
+ if [[ "$_arg" == -chdir=* ]]; then
+ export TFENV_DIR="${PWD}/${_arg#-chdir=}";
+ break;
+ else
+ export TFENV_DIR="${PWD}";
+ fi;
+done;
+log 'debug' "Setting TFENV_DIR to ${TFENV_DIR}";
 
 abort() {
  log 'debug' 'Aborting...';