Enable the ESLint operator-assignment rule

This patch was generated automatically, using the `gulp lint --fix` command.

Please find additional details about the ESLint rule at https://eslint.org/docs/rules/operator-assignment

src/display/canvas.js

@@ -145,10 +145,10 @@ function addContextCurrentTransform(ctx) {
 
   ctx.scale = function ctxScale(x, y) {
     const m = this._transformMatrix;
-    m[0] = m[0] * x;
-    m[1] = m[1] * x;
-    m[2] = m[2] * y;
-    m[3] = m[3] * y;
+    m[0] *= x;
+    m[1] *= x;
+    m[2] *= y;
+    m[3] *= y;
 
     this._originalScale(x, y);
   };