WIP: Migrate test_contour to use dvc

As discussed in #1131, this PR moves the reference figures in fig.contour to use dvc.

Author: michaelgrund

pygmt/tests/test_contour.py

@@ -83,7 +83,7 @@ def test_contour_vec(region):
     y = y.flatten()
     z = (x - 0.5 * (region[0] + region[1])) ** 2 + 4 * y ** 2
     z = np.exp(-z / 10 ** 2 * np.log(2))
-    fig.contour(x=x, y=y, z=z, projection="X4i", region=region, frame="a", pen="")
+    fig.contour(x=x, y=y, z=z, projection="X4c", region=region, frame="a", pen="")
     return fig
 
 
@@ -93,7 +93,7 @@ def test_contour_matrix(data, region):
     Plot data.
     """
     fig = Figure()
-    fig.contour(data=data, projection="X3i", region=region, frame="ag", pen="")
+    fig.contour(data=data, projection="X3c", region=region, frame="ag", pen="")
     return fig
 
 
@@ -104,6 +104,6 @@ def test_contour_from_file(region):
     """
     fig = Figure()
     fig.contour(
-        data=POINTS_DATA, projection="X4i", region=region, frame="af", pen="#ffcb87"
+        data=POINTS_DATA, projection="X4c", region=region, frame="af", pen="#ffcb87"
     )
     return fig