Add RocksJava build to AppVeyor

Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/4843

Differential Revision: D13573607

Pulled By: sagar0

fbshipit-source-id: 0e752992d1d0187cd423f47b53f9b1f80555f8cd

appveyor.yml

@@ -3,7 +3,7 @@ image: Visual Studio 2017
 before_build:
 - md %APPVEYOR_BUILD_FOLDER%\build
 - cd %APPVEYOR_BUILD_FOLDER%\build
-- cmake -G "Visual Studio 15 Win64" -DOPTDBG=1 -DWITH_XPRESS=1 -DPORTABLE=1 ..
+- cmake -G "Visual Studio 15 Win64" -DOPTDBG=1 -DWITH_XPRESS=1 -DPORTABLE=1 -DJNI=1 ..
 - cd ..
 build:
   project: build\rocksdb.sln