remove duplicate alias & update gd

[UncleBill]

• remove duplcate gd
• alias gd='git diff' to alias gd='git diff --color'
• add alias gdcac at @serdardalgic's suggestion

[serdardalgic]

This also catched my eye too. Thanks for the fix, I support getting this fix.
In addition to this, I have a suggestion, I would ask git diff --cached like this:

alias gdcac='git diff --cached'

@UncleBill if you like this too, can you add this into your merge request? I can open a new merge request too, but as I have seen this merge request, I wanted to write this down.

I didn't offer the "gdc" alias, 'cause there is a program called gdc, a D compiler in many linux distros.

Peace!

-Serdar