deps: update dependency com.google.cloud:google-cloud-core to v2.8.21 (#1034)

* deps: update dependency com.google.cloud:google-cloud-core to v2.8.21

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vision/snippets/pom.xml

@@ -66,7 +66,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-core</artifactId>
-      <version>2.8.20</version>
+      <version>2.8.21</version>
       <scope>test</scope>
       <classifier>tests</classifier>
     </dependency>