Correct dependency tag syntax. (GoogleCloudPlatform#1294)

Author: dzlier-gcp

vision/face-detection/pom.xml

@@ -37,7 +37,7 @@
   </properties>
 
   <dependencies>
-    <!-- START face_detection_dependencies -->
+    <!-- [START face_detection_dependencies] -->
     <dependency>
       <groupId>com.google.apis</groupId>
       <artifactId>google-api-services-vision</artifactId>
@@ -59,7 +59,7 @@
       <artifactId>guava</artifactId>
       <version>25.1-android</version>
     </dependency>
-    <!-- END face_detection_dependencies -->
+    <!-- [END face_detection_dependencies] -->
 
     <!-- Test Dependencies -->
     <dependency>