docs: update git credential cache platforms (#1049)

GCM's documentation states that git's credential cache is supported on
Windows. Unfortunately, due to lack of Unix socket support on Windows
versions prior to Windows 10, this feature is not currently supported on
Windows, so this change removes it from the list of platforms on which
this credstore can be used. See [this
issue](git-for-windows/git#3892) for more
details.

Author: ldennington

docs/configuration.md

@@ -442,7 +442,7 @@ _(unset)_|Windows: `wincredman`, macOS: `keychain`, Linux: _(none)_|-
 `keychain`|macOS Keychain.|macOS
 `secretservice`|[freedesktop.org Secret Service API][freedesktop-ss] via [libsecret][libsecret] (requires a graphical interface to unlock secret collections).|Linux
 `gpg`|Use GPG to store encrypted files that are compatible with the [pass][pass] (requires GPG and `pass` to initialize the store).|macOS, Linux
-`cache`|Git's built-in [credential cache][credential-cache].|Windows, macOS, Linux
+`cache`|Git's built-in [credential cache][credential-cache].|macOS, Linux
 `plaintext`|Store credentials in plaintext files (**UNSECURE**). Customize the plaintext store location with [`credential.plaintextStorePath`][credential-plaintextstorepath].|Windows, macOS, Linux
 
 #### Example