Replace tab by white spaces

Author: yvonnefroehlich

pygmt/datasets/earth_dist.py

@@ -68,7 +68,7 @@ def load_earth_dist(
     grid
         The GSHHG Earth distance to shoreline grid. Coordinates are latitude and
         longitude in degrees. Distances are in kilometers, where positive (negative)
-		values mean land to coastline (ocean to coastline).
+        values mean land to coastline (ocean to coastline).
 
     Note
     ----