Modernize recommendation for credential store

GCM for Windows (along with GCM for macOS/Linux) has been replaced with the cross-platform GCM Core.

Author: vtbassmatt

book/07-git-tools/sections/credentials.asc

@@ -19,9 +19,9 @@ Git has a few options provided in the box:
   The downside of this approach is that your passwords are stored in cleartext in a plain file in your home directory.
 * If you're using a Mac, Git comes with an "`osxkeychain`" mode, which caches credentials in the secure keychain that's attached to your system account.
   This method stores the credentials on disk, and they never expire, but they're encrypted with the same system that stores HTTPS certificates and Safari auto-fills.
-* If you're using Windows, you can install a helper called "`Git Credential Manager for Windows.`"
-  This is similar to the "`osxkeychain`" helper described above, but uses the Windows Credential Store to control sensitive information.
-  It can be found at https://github.com/Microsoft/Git-Credential-Manager-for-Windows[].
+* If you're using Windows, macOS, or Linux, you can install a helper called "`Git Credential Manager Core.`"
+  This uses platform-native data stores to control sensitive information.
+  It can be found at https://github.com/microsoft/Git-Credential-Manager-Core[].
 
 You can choose one of these methods by setting a Git configuration value: