Replace deprecated `delim_whitespace=True` by `sep="\s+"` (pandas)

[yvonnefroehlich]

Warning by pandas:

FutureWarning: The 'delim_whitespace' keyword in pd.read_table is deprecated
and will be removed in a future version. Use ``sep='\s+'`` instead

Affected Jupyter notebooks: Please note that in the raw notebook display this looks like sep=\"\\s+\"

• [x] 008_map_scan_tectonic
• [x] 009_paper_GR2020
  • [x] Fig 1
  • [x] Fig 2
  • [x] Fig 4
  • [x] Fig 14
  • [x] Fig S10
  • [x] Fig S17_raw
  • [x] Fig S18

gitnotebook: https://gitnotebooks.com/michaelgrund/GMT-plotting/pull/19