(deps): upgrade to canvas@2, jsdom@15

- because canvas@1 is deprecated and is having install issues
  - see hhttps://travis-ci.org/agilgur5/react-signature-canvas/builds/650962136,
    https://travis-ci.org/agilgur5/react-signature-canvas/builds/658062587,
    etc

Author: agilgur5

jest.config.js

@@ -1,4 +1,6 @@
 module.exports = {
+  // Jest 24 defaults to JSDOM 11, upgrade to 15 to support canvas@2
+  testEnvironment: 'jest-environment-jsdom-fifteen',
   setupFilesAfterEnv: [
     // configure enzyme w/ react adapter
     '<rootDir>/test/config/configure-enzyme.js',

package-lock.json

@@ -63,10 +63,11 @@
     "babel-preset-es2015": "^6.14.0",
     "babel-preset-react": "^6.11.1",
     "babel-preset-stage-2": "^6.13.0",
-    "canvas-prebuilt": "^1.6.11",
+    "canvas": "^2.6.1",
     "css-loader": "^0.24.0",
     "enzyme": "^3.10.0",
     "jest": "^24.8.0",
+    "jest-environment-jsdom-fifteen": "^1.0.2",
     "jest-without-globals": "^0.0.2",
     "react": "^17.0.2",
     "react-dom": "^17.0.2",