Check for git command without the .exe

[gaelcolas]

Filing for consideration/feedback until I raise a PR.

Currently the git.ps1 script checks that git is available by doing a get-command git.exe. https://github.com/RamblingCookieMonster/PSDepend/blob/master/PSDepend/PSDependScripts/Git.ps1#L115-L117

I had an instance where git was not available in Path, but git.cmd was, via chefdk.

Would you accept a pr to change to Get-Command git ?

Thanks, Gael

[RamblingCookieMonster]

Absolutely, works for me!