Small change to compile

[AndyZe]

This is a very small change that allows me to compile on Ubuntu 16.04, 64-bit. I'm using the most up-to-date version of openvr, cloned from https://github.com/ValveSoftware/openvr/tree/b72abcebff7e6c6c70ce8ac8f6a09b70d44397e2

I very much appreciate this work!

[AndyZe]

The error before this change was:

LighthouseTracking.cpp:437:18: error: ‘class vr::IVRSystem’ has no member named ‘IsInputFocusCapturedByAnotherProcess’
  if (vr_pointer->IsInputFocusCapturedByAnotherProcess())

[offchan42]

I have this error to on Windows/Cygwin!

[offchan42]

And also the file was named compile.bat not compile.sh as shown in the README.