Upgrade java client to latest

[thiemf]

Hi,

really like this tool 👍 However, when using it with iOS / Xcode 10.1, currently I get the following error when using e.g. ios.source():
Calling AppiumDriver.execute() with args: ["var source = document.documentElement.outerHTML; \nif (!source) { source = new XMLSerializer().serializeToString(document); }\nreturn source;",[],"6cc6ee89-afbc-46dc-9669-5739b4c800a0"]
[XCUITest] Executing command 'execute'
[W3C (6cc6ee89)] Encountered internal error running command: NotImplementedError: Method is not implemented
[W3C (6cc6ee89)] at XCUITestDriver.extensions.execute (/Applications/Appium.app/Contents/Resources/app/node_modules/appium/node_modules/appium-xcuitest-driver/lib/commands/execute.js:13:11)

When changing the dependency on the appium java client to latest 7.0.0 and building the package by myself on my machine, this seems to solve the issue. Would it be possible to upgrade the appium java client here in the repo?
Thank you.

Cheers