fix import path

Author: marusama

README.md

@@ -17,7 +17,7 @@ Fast resizable golang semaphore based on CAS
 ### Usage
 Initiate
 ```go
-import "github.com/marusama/semaphore"
+import "github.com/marusama/semaphore/v2"
 ...
 sem := semaphore.New(5) // new semaphore with limit = 5
 ```

semaphore.go

@@ -5,7 +5,7 @@
 // Package semaphore provides an implementation of counting semaphore primitive with possibility to change limit
 // after creation. This implementation is based on Compare-and-Swap primitive that in general case works faster
 // than other golang channel-based semaphore implementations.
-package semaphore // import "github.com/marusama/semaphore"
+package semaphore // import "github.com/marusama/semaphore/v2"
 
 import (
 	"context"