Qt 5.6 renames signal QProcesss::error()

Qt 5.6 renames signal QProcesss::error()

QProcesss::error() was renamed to QProcesss::errorOccurred().

The renaming was done to avoid confusion from overloading (see the
documentation for the signal before the renaming [1]).

For more details, see this Qt bug report [2].

[1] http://doc.qt.io/qt-5/qprocess.html#error-1
[2] https://codereview.qt-project.org/#/c/114451/