Fix version inconsistencies across documentation

Update import statements from v5 to v6 and remove deprecated bare parameter from git.PlainClone() calls to align with v6 API changes.

Signed-off-by: Paulo Gomes <pjbgf@linux.com>

Author: pjbgf

src/index.md

@@ -13,12 +13,12 @@ go-git is a highly extensible Git implementation in pure Go. This documentation
 
 ```go
 import (
-    "github.com/go-git/go-git/v5"
+    "github.com/go-git/go-git/v6"
 )
 
 func main() {
     // Clone repository
-    repo, err := git.PlainClone("/path/to/repo", false, &git.CloneOptions{
+    repo, err := git.PlainClone("/path/to/repo", &git.CloneOptions{
         URL: "https://github.com/go-git/go-git",
     })
 }

src/tutorials/getting-started.md

@@ -16,7 +16,7 @@ operations using the latest version of go-git.
 The following example shows how to clone a Git repository to your local filesystem:
 
 ```go
-r, err := git.PlainClone("/path/to/repo", false, &git.CloneOptions{
+r, err := git.PlainClone("/path/to/repo", &git.CloneOptions{
     URL: "https://github.com/go-git/go-git",
 })
 ```