Bump json from 20180130 to 20180813 (#978)

Bumps [json](https://github.com/douglascrockford/JSON-java) from 20180130 to 20180813.
- [Release notes](https://github.com/douglascrockford/JSON-java/releases)
- [Commits](https://github.com/douglascrockford/JSON-java/compare/20180130...20180813

)

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

mobile/build.gradle

@@ -132,7 +132,7 @@ dependencies {
 
     testImplementation 'org.mockito:mockito-core:2.19.1'
     testImplementation 'junit:junit:4.12'
-    testImplementation 'org.json:json:20180130'
+    testImplementation 'org.json:json:20180813'
     testImplementation 'com.squareup.okhttp3:mockwebserver:3.11.0'
 
     // PowerMock