Change "ALT TEXT HERE" in uploader shortcode to ALT_TEXT_HERE

[petele]

Is your feature request related to a problem? Please describe.
After uploading an image using the uploader, it gives you the shortcode you can easily paste into your doc. To update the alt text, I need to highlight three words, the type what I need.

Describe the solution you'd like
Changing the spaces to underscores will make it easy to simply double click to select the text, then start typing my new alt text.