Quickfix min/max elevation for new SRTM15+V2 earth relief grids (#350)

Upstream GMT has updated its earth relief grids to use the new [Tozer et al. 2019](https://doi.org/10.1029/2019EA000658) Global Bathymetry and Topography at 15 Arc Sec (SRTM15+V2) data, see GenericMappingTools/gmt#1846. This resulted in a couple of test failures because of changed minimum/maximum elevation values, which this commit addresses.

Author: weiji14

pygmt/clib/session.py

@@ -107,8 +107,7 @@ class Session:
     ...             ses.call_module("grdinfo", "{} -C ->{}".format(fin, fout.name))
     ...             # Read the contents of the temp file before it's deleted.
     ...             print(fout.read().strip())
-    -180 180 -90 90 -8425 5551 1 1 361 181
-
+    -180 180 -90 90 -8596 5559 1 1 361 181
     """
 
     # The minimum version of GMT required
@@ -1188,15 +1187,15 @@ def virtualfile_from_grid(self, grid):
         >>> print(data.lat.values.min(), data.lat.values.max())
         -90.0 90.0
         >>> print(data.values.min(), data.values.max())
-        -8425.0 5551.0
+        -8596.0 5559.0
         >>> with Session() as ses:
         ...     with ses.virtualfile_from_grid(data) as fin:
         ...         # Send the output to a file so that we can read it
         ...         with GMTTempFile() as fout:
         ...             args = '{} -L0 -Cn ->{}'.format(fin, fout.name)
         ...             ses.call_module('grdinfo', args)
         ...             print(fout.read().strip())
-        -180 180 -90 90 -8425 5551 1 1 361 181
+        -180 180 -90 90 -8596 5559 1 1 361 181
         >>> # The output is: w e s n z0 z1 dx dy n_columns n_rows
 
         """

pygmt/tests/test_datasets.py

@@ -62,8 +62,8 @@ def test_earth_relief_60():
     assert data.shape == (181, 361)
     npt.assert_allclose(data.lat, np.arange(-90, 91, 1))
     npt.assert_allclose(data.lon, np.arange(-180, 181, 1))
-    npt.assert_allclose(data.min(), -8425)
-    npt.assert_allclose(data.max(), 5551)
+    npt.assert_allclose(data.min(), -8596)
+    npt.assert_allclose(data.max(), 5559)
 
 
 def test_earth_relief_30():
@@ -72,5 +72,5 @@ def test_earth_relief_30():
     assert data.shape == (361, 721)
     npt.assert_allclose(data.lat, np.arange(-90, 90.5, 0.5))
     npt.assert_allclose(data.lon, np.arange(-180, 180.5, 0.5))
-    npt.assert_allclose(data.min(), -9214)
-    npt.assert_allclose(data.max(), 5859)
+    npt.assert_allclose(data.min(), -9458)
+    npt.assert_allclose(data.max(), 5888)

pygmt/tests/test_info.py

@@ -59,13 +59,13 @@ def test_grdinfo():
     "Make sure grd info works as expected"
     grid = load_earth_relief()
     result = grdinfo(grid, L=0, C="n")
-    assert result.strip() == "-180 180 -90 90 -8425 5551 1 1 361 181"
+    assert result.strip() == "-180 180 -90 90 -8596 5559 1 1 361 181"
 
 
 def test_grdinfo_file():
     "Test grdinfo with file input"
     result = grdinfo("@earth_relief_60m", L=0, C="n")
-    assert result.strip() == "-180 180 -90 90 -8425 5551 1 1 361 181"
+    assert result.strip() == "-180 180 -90 90 -8596 5559 1 1 361 181"
 
 
 def test_grdinfo_fails():