Update java changelog

Author: shs96c

java/CHANGELOG

@@ -1,3 +1,20 @@
+v3.12.0
+=======
+
+* Added `User-Agent` header to requests from Selenium to give remote
+  ends more visibility into distribution of clients.
+* Remove GSON from how we coerce JSON to Java types.
+* Clean up the internals of Selenium's JSON handling, including
+  deprecating places where GSON leaks from our APIs.
+* Grid assignes node to a random free port if not specified.
+  explicitly. Fixes #5783.
+* Reduced visibility of DriverService.sendOutputTo.
+* Addressed concerns about backward compatability of Grid's `-host`
+  parameter.
+* Implemented WebStorage in ChromeDriver and FirefoxDriver.
+* Documentation clean up in `By`.
+* `before/afterGetScreenshotAs` added to to WebDriverEventListener.
+
 v3.11.0
 =======