fix bad links

Author: tamram

articles/storage/blobs/versioning-overview.md

@@ -221,7 +221,7 @@ If you've changed a blob or version's tier, then you're billed for the entire ob
 
 For more information about billing details for blob snapshots, see [Blob snapshots](snapshots-overview.md).
 
-### Billing when the blob tier hasn't been explicitly set
+### Billing when the blob tier has not been explicitly set
 
 If you have not explicitly set the blob tier for any versions of a blob, then you're charged for unique blocks or pages across all versions, and any snapshots it may have. Data that is shared across blob versions is charged only once. When a blob is updated, then data in the new current version diverges from the data stored in previous versions, and the unique data is charged per block or page.