add canvas for unit tests

Author: Fil

package.json

@@ -29,6 +29,7 @@
     "@observablehq/plot": "./src/index.js"
   },
   "devDependencies": {
+    "canvas": "^2.6.1",
     "d3": "^6.3.1",
     "eslint": "^7.12.1",
     "esm": "^3.2.25",

src/legend.js

@@ -39,16 +39,6 @@ export class ColorLegend {
         tickValues
       } = {}
     } = {} } = this;
-    console.warn({
-      title,
-      tickSize,
-      width,
-      height,
-      top,
-      bottom,
-      left,
-      right
-    });
     const tx = left !== undefined ? left : canvasWidth - width + right;
     const ty = bottom !== undefined ? canvasHeight - bottom - height : top;
     return create("svg:g")

test/output/gistempAnomaly.svg

@@ -13,7 +13,8 @@ export default async function() {
       grid: true
     },
     color: {
-      type: "diverging"
+      type: "diverging",
+      legend: true
     },
     marks: [
       Plot.ruleY([0]),