Figure.coast: Parameter 'shorelines' also accepts bool (#3979)

Fix typo in docs

Author: Esteban82

pygmt/src/coast.py

@@ -154,7 +154,7 @@ def coast(
 
     water : str
         Select filling "wet" areas.
-    shorelines : int, str, or list
+    shorelines : bool, int, str, or list
         [*level*\ /]\ *pen*.
         Draw shorelines [Default is no shorelines]. Append pen attributes
         [Default is ``"0.25p,black,solid"``] which apply to all four levels.