deps: update gax.version to v1.59.1 (#159)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [com.google.api:gax-grpc](https://togithub.com/googleapis/gax-java) | minor | `1.58.2` -> `1.59.1` |
| [com.google.api:gax-bom](https://togithub.com/googleapis/gax-java) | minor | `1.58.2` -> `1.59.1` |

---

### Release Notes

<details>
<summary>googleapis/gax-java</summary>

### [`v1.59.1`](https://togithub.com/googleapis/gax-java/blob/master/CHANGELOG.md#&#8203;1591-httpswwwgithubcomgoogleapisgax-javacomparev1590v1591-2020-10-05)

[Compare Source](https://togithub.com/googleapis/gax-java/compare/v1.59.0...v1.59.1)

### [`v1.59.0`](https://togithub.com/googleapis/gax-java/blob/master/CHANGELOG.md#&#8203;1590-httpswwwgithubcomgoogleapisgax-javacomparev1583v1590-2020-09-28)

[Compare Source](https://togithub.com/googleapis/gax-java/compare/v1.58.3...v1.59.0)

##### Features

-   Allow user-agents to be specified by both internal headers and user headers ([#&#8203;1190](https://www.github.com/googleapis/gax-java/issues/1190)) ([266329e](https://www.github.com/googleapis/gax-java/commit/266329e89642bfc6be579e600d3f995f4416ae4e)), closes [/github.com/googleapis/java-bigtable/pull/404#pullrequestreview-480972135](https://www.github.com/googleapis//github.com/googleapis/java-bigtable/pull/404/issues/pullrequestreview-480972135)

##### Bug Fixes

-   truncate RPC timeouts to time remaining in totalTimeout ([#&#8203;1191](https://www.github.com/googleapis/gax-java/issues/1191)) ([1d0c940](https://www.github.com/googleapis/gax-java/commit/1d0c94061bab124be81a649ac3fa1ce5d9a2df23))

##### Dependencies

-   update guava to 29.0-android ([#&#8203;1174](https://www.github.com/googleapis/gax-java/issues/1174)) ([287cada](https://www.github.com/googleapis/gax-java/commit/287cadae528549545da9e7e9d63fd70c1268e3c1)), closes [#&#8203;1151](https://www.github.com/googleapis/gax-java/issues/1151)

##### [1.58.3](https://www.github.com/googleapis/gax-java/compare/v1.58.2...v1.58.3) (2020-09-15)

##### Bug Fixes

-   [gax-java] Add speedy Bazel builds to Travis ([#&#8203;1181](https://www.github.com/googleapis/gax-java/issues/1181)) ([2fb85fe](https://www.github.com/googleapis/gax-java/commit/2fb85fed095c6043ee39b63a0f7dff3fd93cbd7b))
-   [gax-java] add Vim files to .gitignore ([#&#8203;1179](https://www.github.com/googleapis/gax-java/issues/1179)) ([2de22b6](https://www.github.com/googleapis/gax-java/commit/2de22b6645fbfd7ada7d0067e5cdd3c2039ec190))
-   [gax-java] Fix broken Bazel build ([#&#8203;1180](https://www.github.com/googleapis/gax-java/issues/1180)) ([834c05e](https://www.github.com/googleapis/gax-java/commit/834c05e1d35a17f90bf8cd1b2cdce40bea451c95))

##### [1.58.2](https://www.github.com/googleapis/gax-java/compare/v1.58.1...v1.58.2) (2020-08-07)

##### Bug Fixes

-   Settings objects should not try to read quotaProjectId from credentials ([#&#8203;1162](https://www.github.com/googleapis/gax-java/issues/1162)) ([1b09bcf](https://www.github.com/googleapis/gax-java/commit/1b09bcff1ddfaed8cfa58b92c787f8fc9b08abef))

##### [1.58.1](https://www.github.com/googleapis/gax-java/compare/v1.58.0...v1.58.1) (2020-08-06)

##### Bug Fixes

-   fix dependencies.properties resource file creation during deployment ([#&#8203;1163](https://www.github.com/googleapis/gax-java/issues/1163)) ([3e7e1f1](https://www.github.com/googleapis/gax-java/commit/3e7e1f1e64bdeb23a51b5155faea975beec0bc84))
-   Watchdog.shutdownNow() does not shutdown executor ([#&#8203;1158](https://www.github.com/googleapis/gax-java/issues/1158)) ([6241a21](https://www.github.com/googleapis/gax-java/commit/6241a2118690d07dd28ffb9447423363f3f914e4))

### [`v1.58.3`](https://togithub.com/googleapis/gax-java/blob/master/CHANGELOG.md#&#8203;1583-httpswwwgithubcomgoogleapisgax-javacomparev1582v1583-2020-09-15)

[Compare Source](https://togithub.com/googleapis/gax-java/compare/v1.58.2...v1.58.3)

</details>

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pom.xml

@@ -56,7 +56,7 @@
     <site.installationModule>${project.artifactId}</site.installationModule>
 
     <grpc.version>1.32.1</grpc.version>
-    <gax.version>1.58.2</gax.version>
+    <gax.version>1.59.1</gax.version>
     <guava.version>29.0-android</guava.version>
     <protobuf.version>3.13.0</protobuf.version>
     <google.api-common.version>1.10.0</google.api-common.version>