Bump gson from 2.8.5 to 2.8.6

Bumps [gson](https://github.com/google/gson) from 2.8.5 to 2.8.6.
- [Release notes](https://github.com/google/gson/releases)
- [Changelog](https://github.com/google/gson/blob/master/CHANGELOG.md)
- [Commits](google/gson@gson-parent-2.8.5...gson-parent-2.8.6)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

exonum-java-binding/pom.xml

@@ -122,7 +122,7 @@
     <vertx.version>3.8.2</vertx.version>
     <equalsverifier.version>3.1.10</equalsverifier.version>
     <javax-annotation-api.version>1.3.2</javax-annotation-api.version>
-    <gson.version>2.8.5</gson.version>
+    <gson.version>2.8.6</gson.version>
     <auto-value-gson.version>1.0.0</auto-value-gson.version>
     <!-- Default values of properties set by Jacoco when coverage is enabled.
          Passed to the JVM running tests. -->