Fix formatting issue

Author: seisman

pygmt/src/blockm.py

@@ -230,7 +230,7 @@ def blockmedian(data=None, x=None, y=None, z=None, outfile=None, **kwargs):
     -------
     >>> import pygmt  # doctest: +SKIP
     >>> # Load a table of ship observations of bathymetry off Baja California
-    >>> data = pygmt.datasets.load_sample_data(name='bathymetry')
+    >>> data = pygmt.datasets.load_sample_data(name="bathymetry")
     >>> # Calculate block median values within 5 by 5 minute bins
     >>> data_bmedian = pygmt.blockmedian(
     ...     data=data, region=[245, 255, 20, 30], spacing="5m"