LongPress second fix

[JohannAtGithub]

Description

While trying to use

TouchAction action = new TouchAction(driver);
action.LongPress(100, 100).Perform();

following error occurred:

"[AndroidDriver] Error: unknown action longpress"

This error got already fixed in issue #180, but only in one of two cases in the code.
To fix this issue you need to change "longpress" to longPress" in the TouchAction class.

Environment

• .NET Framework version 4.7
• Appium version v1.7.1
• Node.js version 6.11.0