fix axis margin option (#1484)

Author: mbostock

src/marks/axis.js

@@ -78,10 +78,11 @@ function axisKy(
     tickPadding,
     tickRotate,
     x,
-    marginTop = 20,
-    marginRight = anchor === "right" ? 40 : 0,
-    marginBottom = 20,
-    marginLeft = anchor === "left" ? 40 : 0,
+    margin,
+    marginTop = margin === undefined ? 20 : margin,
+    marginRight = margin === undefined ? (anchor === "right" ? 40 : 0) : margin,
+    marginBottom = margin === undefined ? 20 : margin,
+    marginLeft = margin === undefined ? (anchor === "left" ? 40 : 0) : margin,
     label,
     labelOffset,
     labelAnchor,
@@ -180,10 +181,11 @@ function axisKx(
     tickPadding,
     tickRotate,
     y,
-    marginTop = anchor === "top" ? 30 : 0,
-    marginRight = 20,
-    marginBottom = anchor === "bottom" ? 30 : 0,
-    marginLeft = 20,
+    margin,
+    marginTop = margin === undefined ? (anchor === "top" ? 30 : 0) : margin,
+    marginRight = margin === undefined ? 20 : margin,
+    marginBottom = margin === undefined ? (anchor === "bottom" ? 30 : 0) : margin,
+    marginLeft = margin === undefined ? 20 : margin,
     label,
     labelAnchor,
     labelOffset,