Fix Git description to make base conf be N/A

[otahi]

I have corrected the incorrect description for Git.

---

Before

Application	Base conf.	Specific conf.	Env. var.
configure_apt_proxy	config.proxy.*	config.apt_proxy.*	VAGRANTAPT*
configure_git_proxy	config.proxy.*	config.git_proxy.*	VAGRANTGIT*
configure_svn_proxy	N/A	config.svn_proxy.*	VAGRANTSVN*
configure_yum_proxy	config.proxy.*	config.yum_proxy.*	VAGRANTYUM*

:arrow_down:

After

Application	Base conf.	Specific conf.	Env. var.
configure_apt_proxy	config.proxy.*	config.apt_proxy.*	VAGRANTAPT*
configure_git_proxy	N/A	config.git_proxy.*	VAGRANTGIT*
configure_svn_proxy	N/A	config.svn_proxy.*	VAGRANTSVN*
configure_yum_proxy	config.proxy.*	config.yum_proxy.*	VAGRANTYUM*

---

configure_git_proxy.rb#L18

        # @return [Vagrant::Plugin::V2::Config] the configuration
        def config
          return @config if @config

          # Use only `config.git_proxy`, don't merge with the default config
          @config = @machine.config.git_proxy
          finalize_config(@config)
        end