Fix typo in docstring

Author: juliohm

src/domains/meshes/regulargrid.jl

@@ -28,7 +28,7 @@ point using a given `spacing`.
 ```
 RegularGrid((10, 20), Point(LatLon(30.0°, 60.0°)), (1.0, 1.0)) # add coordinate units to spacing
 RegularGrid((10, 20), Point(Polar(0.0cm, 0.0rad)), (10.0mm, 1.0rad)) # convert spacing units to coordinate units
-RegularGrid((10, 20), Point(Marcator(0.0, 0.0)), (1.5, 1.5))
+RegularGrid((10, 20), Point(Mercator(0.0, 0.0)), (1.5, 1.5))
 RegularGrid((10, 20, 30), Point(Cylindrical(0.0, 0.0, 0.0)), (3.0, 2.0, 1.0))
 ```