Fixed issue with using the Screenshot service on a Mac.

Prior to this fix setting screenshots from devices would result in the following exception:

Exception in thread "main" java.lang.UnsatisfiedLinkError: Unable to load library 'imobiledevice-sdk': dlopen(libimobiledevice-sdk.dylib, 9): image not found
	at com.sun.jna.NativeLibrary.loadLibrary(NativeLibrary.java:169)
	at com.sun.jna.NativeLibrary.getInstance(NativeLibrary.java:242)
	at com.sun.jna.NativeLibrary.getInstance(NativeLibrary.java:205)
	at org.libimobiledevice.ios.driver.binding.raw.ImobiledeviceSdkLibrary.<clinit>(ImobiledeviceSdkLibrary.java:25)
	at org.libimobiledevice.ios.driver.binding.services.IOSDevice.<init>(IOSDevice.java:44)
	at org.libimobiledevice.ios.driver.binding.services.DeviceService.get(DeviceService.java:37)
	at IosDriverTest.runTest(IosDriverTest.java:66)
	at IosDriverTest.main(IosDriverTest.java:23)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)