chore(deps): update dependency com.google.cloud:google-cloud-retail to v2.0.15 (#373)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.cloud:google-cloud-retail](https://togithub.com/googleapis/java-) | `2.0.14` -> `2.0.15` | [![age](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-retail/2.0.15/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-retail/2.0.15/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-retail/2.0.15/compatibility-slim/2.0.14)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-retail/2.0.15/confidence-slim/2.0.14)](https://docs.renovatebot.com/merge-confidence/) |

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retail/interactive-tutorials/pom.xml

@@ -41,7 +41,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-retail</artifactId>
-      <version>2.0.14</version>
+      <version>2.0.15</version>
     </dependency>
     <dependency>
       <groupId>junit</groupId>