Using string command parameters (--thing="value") is escaping the quotes in the value.

To Reproduce

> git --git-dir=.git rev-parse --show-toplevel
/my/project

> git --git-dir=".git" rev-parse --show-toplevel
fatal: not a git repository: '".git"'

Note the double quotes surrounding the --git-dir parameter in the second example.

Expected behavior
Both examples are functionally the same - I should be able to surround the string with quotes, and they should not be escaped (included as part of the value itself).

Configuration (please complete the following information):

• OS: macOS 10.15.5
• Nu version: 0.15.0
• Optional features (if any): All stable features