installation: fix for typos in install doc
installation: fix for typos in install doc

Signed-off-by: Gilles Louppe <0e4788c4e7299c60f7a4c37191a19118750c9f4f@gmail.com>

tiborsimko/invenio,inveniosoftware/invenio,inveniosoftware/invenio,tiborsimko/invenio