Do not print credentials in console

[sangee2004]

gptscript version v0.8.1+da33973d

Steps to reproduce the problem:

1. Have OpenAI API token already set (sys.openai credential created) by executing any gptscript.
2. Execute the following script that uses gpt4-v-vision and dalle-image-generation tools.

Tools:  github.com/gptscript-ai/gpt4-v-vision, github.com/gptscript-ai/dalle-image-generation, sys.download

Generate an image of cow and download it in cow.png
Describe the image in file://./cow.png like a kindergarten teacher would.

3. Notice that when user is prompted for entering the credentials for gpt4-v-vision and dalle-image-generation tools , the credentials are printed in clear text in console

12:33:35 started  [vision(6)] [input={"images":"file://./cow.png","prompt":"Describe the image like a kindergarten teacher would."}]
12:33:35 started  [credential: github.com/gptscript-ai/gpt4-v-vision/credential]
12:33:35 sent     [credential: github.com/gptscript-ai/gpt4-v-vision/credential]
Please enter your OpenAI API token.
? token ***************************************************
12:34:06 ended    [credential: github.com/gptscript-ai/gpt4-v-vision/credential] [output={\"env\": {\"OPENAI_API_KEY\": \"sk-*******************\"}}] ==> This is in clear text
12:34:06 sent     [vision(6)]
12:34:19 ended    [vision(6)] [output={\n    \"id\": \"chatcmpl-9Z1Xv5M9by6w4lA34VOUnPj5zbepX\",\n    \"object\": \"chat.completion\",\n    \"created\"...]

[sangee2004]

Tokens are also logged in clear text in "Stack Trace View" option when executing scripts using Chat Builder using "--ui" option.

[sangee2004]

Tested with gptscript version v0.0.0-dev-f8d3b44e-dirty

Tokens are not logged in TUI and in "Stack Trace View" option anymore.