Plot vertical help lines in one plot call

Co-authored-by: Dongdong Tian <seisman.info@gmail.com>

Author: yvonnefroehlich

pygmt/src/pygmtlogo.py

@@ -249,8 +249,7 @@ def _vline_coords(gap=0):
         fig.plot(x=0, y=0, style=f"c{2 * (r2 + (r3 - r4))}c", pen="0.3p,gray30,2_2")
         # Lines for letter M
         fig.hlines(y=[r4, r5], pen="0.3p,gray30,2_2")
-        fig.vlines(x=r4, pen="0.3p,gray30,2_2")
-        fig.vlines(x=(thick_gap + r4) / 2, pen="0.3p,gray30,2_2")
+        fig.vlines(x=[r4, (thick_gap + r4) / 2], pen="0.3p,gray30,2_2")
 
     # fig.show()
     fig_name_logo = "pygmt_logo"