build(deps): update dependency com.google.cloud:google-cloud-shared-config to v0.6.0 (#136)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [com.google.cloud:google-cloud-shared-config](https://togithub.com/googleapis/java-shared-config) | minor | `0.5.0` -> `0.6.0` |

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### Release Notes

<details>
<summary>googleapis/java-shared-config</summary>

### [`v0.6.0`](https://togithub.com/googleapis/java-shared-config/blob/master/CHANGELOG.md#&#8203;060-httpswwwgithubcomgoogleapisjava-shared-configcomparev050v060-2020-05-19)

[Compare Source](https://togithub.com/googleapis/java-shared-config/compare/v0.5.0...v0.6.0)

##### Features

-   add new configuration necessary to support auto-value ([#&#8203;136](https://www.github.com/googleapis/java-shared-config/issues/136)) ([c14689b](https://www.github.com/googleapis/java-shared-config/commit/c14689b8791c173687f719d73156a989aedd7ba6))

</details>

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google-cloud-datastore-bom/pom.xml

@@ -8,7 +8,7 @@
   <parent>
     <groupId>com.google.cloud</groupId>
     <artifactId>google-cloud-shared-config</artifactId>
-    <version>0.5.0</version>
+    <version>0.6.0</version>
   </parent>
 
   <name>Google Cloud datastore BOM</name>

pom.xml

@@ -14,7 +14,7 @@
   <parent>
     <groupId>com.google.cloud</groupId>
     <artifactId>google-cloud-shared-config</artifactId>
-    <version>0.5.0</version>
+    <version>0.6.0</version>
   </parent>
 
   <developers>