deps: update dependencies (#51)

All updates:

| Package | Update | Change |
|---|---|---|
| `com.google.auth:google-auth-library-credentials` | minor | `0.18.0` -> `0.19.0` |
| `com.google.auto.value:auto-value` (jdk 1.8+) | minor | `1.6.6` -> `1.7` |
| `com.google.auto.value:auto-value-annotations` | minor | `1.6.6` -> `1.7` |
| [com.google.api:gax-bom](https://togithub.com/googleapis/gax-java) ([source](https://togithub.com/googleapis/gax-java)) | minor | `1.51.0` -> `1.52.0` |
| [com.google.api:gax-grpc](https://togithub.com/googleapis/gax-java) ([source](https://togithub.com/googleapis/gax-java)) | minor | `1.51.0` -> `1.52.0` |
| [com.google.cloud:google-cloud-core-grpc](https://togithub.com/googleapis/google-cloud-java/tree/master/google-cloud-clients/google-cloud-core-grpc) | minor | `1.91.3` -> `1.92.0` |
| [com.google.cloud:google-cloud-core](https://togithub.com/googleapis/google-cloud-java/tree/master/google-cloud-clients/google-cloud-core) | minor | `1.91.3` -> `1.92.0` |

**manually copied and merged from the following PRs**
* deps: update gax.version to v1.52.0 #49
* deps: update google.core.version to v1.92.0 #50

pom.xml

@@ -152,10 +152,10 @@
     <github.global.server>github</github.global.server>
     <site.installationModule>google-cloud-firestore-parent</site.installationModule>
     <project.javadoc.protobufBaseURL>https://googleapis.dev/java/google-api-grpc/latest</project.javadoc.protobufBaseURL>
-    <google.core.version>1.91.3</google.core.version>
+    <google.core.version>1.92.0</google.core.version>
     <google.api-common.version>1.8.1</google.api-common.version>
     <google.common-protos.version>1.17.0</google.common-protos.version>
-    <gax.version>1.51.0</gax.version>
+    <gax.version>1.52.0</gax.version>
     <grpc.version>1.25.0</grpc.version>
     <protobuf.version>3.11.1</protobuf.version>
     <junit.version>4.12</junit.version>
@@ -361,7 +361,7 @@
         <jdk>1.7</jdk>
       </activation>
       <properties>
-        <auto-value-annotation.version>1.6.6</auto-value-annotation.version>
+        <auto-value-annotation.version>1.7</auto-value-annotation.version>
         <auto-value.version>1.4</auto-value.version>
       </properties>
     </profile>
@@ -372,7 +372,7 @@
         <jdk>[1.8,)</jdk>
       </activation>
       <properties>
-        <auto-value.version>1.6.6</auto-value.version>
+        <auto-value.version>1.7</auto-value.version>
         <auto-value-annotation.version>${auto-value.version}</auto-value-annotation.version>
       </properties>
     </profile>