Tfenv: 添加“-no-color”选项

你好，

首先，我只想说我喜欢 tfenv 并感谢您花时间创建它。

我在 AWS CodeBuild 中使用 tfenv 并且拥有与 Terraform 相同的“-no-color”选项会很好，因为现在命令输出如下所示：

·[0;32m[INFO] Installing Terraform v0.12.3·[0;39m 
·[0;32m[INFO] Downloading release tarball from https://releases.hashicorp.com/terraform/0.12.3/terraform_0.12.3_linux_amd64.zip·[0;39m 

                                                                           0.6% 
###################################                                       48.9% 
######################################################################## 100.0% 
·[0;32m[INFO] Downloading SHA hash file from https://releases.hashicorp.com/terraform/0.12.3/terraform_0.12.3_SHA256SUMS·[0;39m 
tfenv: tfenv-install: ·[0;33m[WARN] No keybase install found, skipping OpenPGP signature verification·[0;39m 
Archive:  tfenv_download.GiiMAo/terraform_0.12.3_linux_amd64.zip 
  inflating: /************/.tfenv/versions/0.12.3/terraform   
·[0;32m[INFO] Installation of terraform v0.12.3 successful·[0;39m 
·[0;32m[INFO] Switching to v0.12.3·[0;39m 
·[0;32m[INFO] Switching completed·[0;39m

谢谢，
斯坦