blockmean & blockmode: Fix the alias of 'd' to 'nodata' (#1563)

The alias of d is nodata in other modules, but was incorrectly set to data in blockmean and blockmode. This PR fixes the problem.

blockmode was wrapped in #1456 (after v0.4.1), blockmean was wrapped in #1092 but the wrong alias was added in #1500 (after v0.4.1). Thus, the change won't go into the deprecation cycle.

pygmt/src/blockm.py

@@ -72,7 +72,7 @@ def _blockm(block_method, table, outfile, x, y, z, **kwargs):
     V="verbose",
     a="aspatial",
     b="binary",
-    d="data",
+    d="nodata",
     e="find",
     f="coltypes",
     h="header",
@@ -232,7 +232,7 @@ def blockmedian(table=None, outfile=None, *, x=None, y=None, z=None, **kwargs):
     V="verbose",
     a="aspatial",
     b="binary",
-    d="data",
+    d="nodata",
     e="find",
     f="coltypes",
     h="header",