Fixed an improper Linux file path in shadow.test.ouput.OutputTest.run()

Several tests in `shadow.test.ouput.OutputTest` failed to run on Linux due to an `IOException`. This problem occured in all methods/tests where the `run(...)` method (which looks for `a.out` on non-Windows systems) was called. In it's output, the exception stated that `a.out` could not be found.

Within `run(...)`, `ProcessBuilder` was originally being passed `a.out` as the path to the binary file to be executed. According to [it's documentation](http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/ProcessBuilder.html), `ProcessBuilder` requires OS-specific commands. On Linux (and other Unix-based systems), files in the current directory must be prefixed with `./`, otherwise the system's `$PATH` will be searched instead. Thus, `a.out` has been corrected to `./a.out` for non-Windows systems.

All five methods calling `run(...)` now execute properly. However, it is worth noting that `testArray()` and `testArrayList()` now fail due to incorrect output.