fix: replace yaml frontmatter tags with tag (#2353)

localization/vi/abstract-document/README.md

@@ -2,7 +2,7 @@
 title: Abstract Document
 category: Structural
 language: vi
-tags: 
+tag: 
  - Extensibility
 ---
 

localization/vi/abstract-factory/README.md

@@ -2,7 +2,7 @@
 title: Abstract Factory
 category: Creational
 language: vi
-tags:
+tag:
  - Gang of Four
 ---
 

localization/vi/active-object/README.md

@@ -2,7 +2,7 @@
 title: Active Object
 category: Concurrency
 language: vi
-tags:
+tag:
  - Performance
 ---