[firedrake] firedrake compile error

[Buesing, Henrik]

> > > A firedrake-clean aborted with
> > >
> > > / /
> > >
> > > /ImportError:
> > > /home/hbuesing/.local/lib/python2.7/site-packages/petsc4py/lib/arch-
> > > li
> > nux2-c-opt/PETSc.so:
> > >
> > >
> > undefined symbol: SNESSetConvergedReason/
> >
> > This looks like you've updated petsc and not petsc4py, or vice versa.
> 
> [Buesing, Henrik] That's true. I didn't update PETSc. I will do that.

After updating PETSc this also works. 

Henrik