CI: pin build to use pyarrow==1.0
closes #37306

@jorisvandenbossche picked build at random. we can discuss here what the preferences are? cc @jreback 
thanks @simonjayhawkins  We should maybe try to get some of the builds that are now in practice using 1.0 (but not pinned) or pinned to 0.15 to use pyarrow 2.0, because we now only have one build with pyarrow 2.0 (the windows 3.8 one). For some reason the Travis builds are using 1.0, although they are not pinned.
